diff --git a/.gitignore b/.gitignore
index 53113035..f25cbffd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -27,6 +27,8 @@ plugin/**/dist
 
 plugin/oneapi/test/fixtures/modules/*/oneapi
 plugin/dal/test/fixtures/modules/*/dal/
+core/dal-runtime/test/fixtures/modules/*/dal
+!core/dal-runtime/test/fixtures/modules/generate_codes_not_overwrite_dao/dal/dao/FooDAO.ts
 
 plugin/tegg/test/fixtures/apps/**/*.js
 !core/common-util/test/fixtures/**/node_modules
diff --git a/core/dal-runtime/src/CodeGenerator.ts b/core/dal-runtime/src/CodeGenerator.ts
index 7140bd3b..a4980fad 100644
--- a/core/dal-runtime/src/CodeGenerator.ts
+++ b/core/dal-runtime/src/CodeGenerator.ts
@@ -94,16 +94,19 @@ export class CodeGenerator {
       templates: Templates.BASE_DAO,
       filePath: paths.baseBizDAO,
       beautify: true,
+      overwrite: true,
     }, {
       templates: Templates.DAO,
       filePath: paths.bizDAO,
       beautify: true,
+      overwrite: false,
     }, {
       templates: Templates.EXTENSION,
       filePath: paths.extension,
       beautify: false,
+      overwrite: true,
     }];
-    for (const { templates, filePath, beautify } of codes) {
+    for (const { templates, filePath, beautify, overwrite } of codes) {
       await fs.mkdir(path.dirname(filePath), {
         recursive: true,
       });
@@ -127,6 +130,14 @@ export class CodeGenerator {
         .replace(/Partial( )*<( )*(.+?)( )*>/g, 'Partial<$3>')
         .replace(/DataSource( )*<( )*(.+?)( )*>/g, 'DataSource<$3>')
         .replace(/ \? :/g, '?:');
+      if (overwrite !== true) {
+        try {
+          await fs.access(filePath);
+          continue;
+        } catch {
+          // file not exists
+        }
+      }
       await fs.writeFile(filePath, beautified, 'utf8');
     }
   }
diff --git a/core/dal-runtime/test/CodeGenerator.test.ts b/core/dal-runtime/test/CodeGenerator.test.ts
index 39a16036..ebbc2b9a 100644
--- a/core/dal-runtime/test/CodeGenerator.test.ts
+++ b/core/dal-runtime/test/CodeGenerator.test.ts
@@ -1,5 +1,6 @@
 import assert from 'node:assert';
 import path from 'node:path';
+import fs from 'node:fs/promises';
 import { Foo } from './fixtures/modules/generate_codes/Foo';
 import { MultiPrimaryKey } from './fixtures/modules/generate_codes/MultiPrimaryKey';
 import { TableModel } from '@eggjs/dal-decorator';
@@ -19,4 +20,19 @@ describe('test/CodeGenerator.test.ts', () => {
     await generator.generate(multiPrimaryKeyTableModel);
     assert(fooModel);
   });
+
+  it('should not overwrite Dao file', async () => {
+    const generator = new CodeGenerator({
+      moduleDir: path.join(__dirname, './fixtures/modules/generate_codes_not_overwrite_dao'),
+      moduleName: 'dal',
+      dalPkg: '@eggjs/dal-decorator',
+    });
+    const fooModel = TableModel.build(Foo);
+    await generator.generate(fooModel);
+
+    const multiPrimaryKeyTableModel = TableModel.build(MultiPrimaryKey);
+    await generator.generate(multiPrimaryKeyTableModel);
+    const daoFile = await fs.readFile(path.join(__dirname, './fixtures/modules/generate_codes_not_overwrite_dao/dal/dao/FooDAO.ts'), 'utf8');
+    assert(/customFind/.test(daoFile));
+  });
 });
diff --git a/core/dal-runtime/test/fixtures/modules/generate_codes_not_overwrite_dao/Foo.ts b/core/dal-runtime/test/fixtures/modules/generate_codes_not_overwrite_dao/Foo.ts
new file mode 100644
index 00000000..5e1a3493
--- /dev/null
+++ b/core/dal-runtime/test/fixtures/modules/generate_codes_not_overwrite_dao/Foo.ts
@@ -0,0 +1,323 @@
+import {
+  Column,
+  ColumnType,
+  Geometry,
+  GeometryCollection,
+  Index,
+  IndexType,
+  Line,
+  IndexStoreType,
+  MultiLine,
+  MultiPoint,
+  MultiPolygon,
+  Point,
+  Polygon,
+  Table,
+} from '@eggjs/dal-decorator';
+
+@Table({
+  name: 'egg_foo',
+  comment: 'foo table',
+  // autoExtendSize: 1024,
+  // autoIncrement: 100,
+  // avgRowLength: 1024,
+  characterSet: 'utf8mb4',
+  collate: 'utf8mb4_unicode_ci',
+  // compression: CompressionType.ZLIB,
+  // encryption: true,
+  // engine: 'NDB',
+  // engineAttribute: '{"key":"value"}',
+  // secondaryEngineAttribute: '{"key2":"value2"}',
+  // insertMethod: InsertMethod.FIRST,
+  // keyBlockSize: 1024,
+  // maxRows: 1000000,
+  // minRows: 100,
+  // rowFormat: RowFormat.COMPRESSED,
+})
+@Index({
+  keys: [ 'name', 'col1' ],
+  type: IndexType.UNIQUE,
+  storeType: IndexStoreType.BTREE,
+  comment: 'index comment\n',
+  // engineAttribute: '{"key":"value"}',
+  // secondaryEngineAttribute: '{"key2":"value2"}',
+})
+@Index({
+  keys: [ 'col1' ],
+  type: IndexType.FULLTEXT,
+  comment: 'index comment\n',
+  // engineAttribute: '{"key":"value"}',
+  // secondaryEngineAttribute: '{"key2":"value2"}',
+  // parser: 'foo',
+})
+export class Foo {
+  @Column({
+    type: ColumnType.INT,
+  }, {
+    primaryKey: true,
+    autoIncrement: true,
+    comment: 'the primary key',
+  })
+  id: number;
+
+  @Column({
+    type: ColumnType.VARCHAR,
+    length: 100,
+  }, {
+    uniqueKey: true,
+  })
+  name: string;
+
+  @Column({
+    type: ColumnType.VARCHAR,
+    length: 100,
+  }, {
+    name: 'col1',
+  })
+  col1: string;
+
+  @Column({
+    type: ColumnType.BIT,
+    length: 10,
+  })
+  bitColumn: Buffer;
+
+  @Column({
+    type: ColumnType.BOOL,
+  })
+  boolColumn: 0 | 1;
+
+  @Column({
+    type: ColumnType.TINYINT,
+    length: 5,
+    unsigned: true,
+    zeroFill: true,
+  })
+  tinyIntColumn: number;
+
+  @Column({
+    type: ColumnType.SMALLINT,
+    length: 5,
+    unsigned: true,
+    zeroFill: true,
+  })
+  smallIntColumn: number;
+
+  @Column({
+    type: ColumnType.MEDIUMINT,
+    length: 5,
+    unsigned: true,
+    zeroFill: true,
+  })
+  mediumIntColumn: number;
+
+  @Column({
+    type: ColumnType.INT,
+    length: 5,
+    unsigned: true,
+    zeroFill: true,
+  })
+  intColumn: number;
+
+  @Column({
+    type: ColumnType.BIGINT,
+    length: 5,
+    unsigned: true,
+    zeroFill: true,
+  })
+  bigIntColumn: string;
+
+  @Column({
+    type: ColumnType.DECIMAL,
+    length: 10,
+    fractionalLength: 5,
+    unsigned: true,
+    zeroFill: true,
+  })
+  decimalColumn: string;
+
+  @Column({
+    type: ColumnType.FLOAT,
+    length: 10,
+    fractionalLength: 5,
+    unsigned: true,
+    zeroFill: true,
+  })
+  floatColumn: number;
+
+  @Column({
+    type: ColumnType.DOUBLE,
+    length: 10,
+    fractionalLength: 5,
+    unsigned: true,
+    zeroFill: true,
+  })
+  doubleColumn: number;
+
+  @Column({
+    type: ColumnType.DATE,
+  })
+  dateColumn: Date;
+
+  @Column({
+    type: ColumnType.DATETIME,
+    precision: 3,
+  })
+  dateTimeColumn: Date;
+
+  @Column({
+    type: ColumnType.TIMESTAMP,
+    precision: 3,
+  })
+  timestampColumn: Date;
+
+  @Column({
+    type: ColumnType.TIME,
+    precision: 3,
+  })
+  timeColumn: string;
+
+  @Column({
+    type: ColumnType.YEAR,
+  })
+  yearColumn: number;
+
+  @Column({
+    type: ColumnType.VARCHAR,
+    length: 100,
+    characterSet: 'utf8mb4',
+    collate: 'utf8mb4_unicode_ci',
+  })
+  varCharColumn: string;
+
+  @Column({
+    type: ColumnType.BINARY,
+  })
+  binaryColumn: Buffer;
+
+  @Column({
+    type: ColumnType.VARBINARY,
+    length: 100,
+  })
+  varBinaryColumn: Buffer;
+
+  @Column({
+    type: ColumnType.TINYBLOB,
+  })
+  tinyBlobColumn: Buffer;
+
+  @Column({
+    type: ColumnType.TINYTEXT,
+    characterSet: 'utf8mb4',
+    collate: 'utf8mb4_unicode_ci',
+  })
+  tinyTextColumn: string;
+
+  @Column({
+    type: ColumnType.BLOB,
+    length: 100,
+  })
+  blobColumn: Buffer;
+
+  @Column({
+    type: ColumnType.TEXT,
+    length: 100,
+    characterSet: 'utf8mb4',
+    collate: 'utf8mb4_unicode_ci',
+  })
+  textColumn: string;
+
+  @Column({
+    type: ColumnType.MEDIUMBLOB,
+  })
+  mediumBlobColumn: Buffer;
+
+  @Column({
+    type: ColumnType.LONGBLOB,
+  })
+  longBlobColumn: Buffer;
+
+  @Column({
+    type: ColumnType.MEDIUMTEXT,
+    characterSet: 'utf8mb4',
+    collate: 'utf8mb4_unicode_ci',
+  })
+  mediumTextColumn: string;
+
+  @Column({
+    type: ColumnType.LONGTEXT,
+    characterSet: 'utf8mb4',
+    collate: 'utf8mb4_unicode_ci',
+  })
+  longTextColumn: string;
+
+  @Column({
+    type: ColumnType.ENUM,
+    enums: [ 'A', 'B' ],
+    characterSet: 'utf8mb4',
+    collate: 'utf8mb4_unicode_ci',
+  })
+  enumColumn: string;
+
+  @Column({
+    type: ColumnType.SET,
+    enums: [ 'A', 'B' ],
+    characterSet: 'utf8mb4',
+    collate: 'utf8mb4_unicode_ci',
+  })
+  setColumn: string;
+
+  @Column({
+    type: ColumnType.GEOMETRY,
+    // SRID: 4326,
+  })
+  geometryColumn: Geometry;
+
+
+  @Column({
+    type: ColumnType.POINT,
+    // SRID: 4326,
+  })
+  pointColumn: Point;
+
+  @Column({
+    type: ColumnType.LINESTRING,
+    // SRID: 4326,
+  })
+  lineStringColumn: Line;
+
+  @Column({
+    type: ColumnType.POLYGON,
+    // SRID: 4326,
+  })
+  polygonColumn: Polygon;
+
+  @Column({
+    type: ColumnType.MULTIPOINT,
+    // SRID: 4326,
+  })
+  multipointColumn: MultiPoint;
+
+  @Column({
+    type: ColumnType.MULTILINESTRING,
+    // SRID: 4326,
+  })
+  multiLineStringColumn: MultiLine;
+
+  @Column({
+    type: ColumnType.MULTIPOLYGON,
+    // SRID: 4326,
+  })
+  multiPolygonColumn: MultiPolygon;
+
+  @Column({
+    type: ColumnType.GEOMETRYCOLLECTION,
+    // SRID: 4326,
+  })
+  geometryCollectionColumn: GeometryCollection;
+
+  @Column({
+    type: ColumnType.JSON,
+  })
+  jsonColumn: object;
+}
diff --git a/core/dal-runtime/test/fixtures/modules/generate_codes_not_overwrite_dao/dal/dao/FooDAO.ts b/core/dal-runtime/test/fixtures/modules/generate_codes_not_overwrite_dao/dal/dao/FooDAO.ts
new file mode 100644
index 00000000..f6d7956f
--- /dev/null
+++ b/core/dal-runtime/test/fixtures/modules/generate_codes_not_overwrite_dao/dal/dao/FooDAO.ts
@@ -0,0 +1,17 @@
+import { SingletonProto, AccessLevel } from '@eggjs/tegg';
+import { BaseFooDAO } from './base/BaseFooDAO';
+
+/**
+ * FooDAO 类
+ * @class FooDAO
+ * @classdesc 在此扩展关于 Foo 数据的一切操作
+ * @extends BaseFooDAO
+ */
+@SingletonProto({
+  accessLevel: AccessLevel.PUBLIC,
+})
+export default class FooDAO extends BaseFooDAO {
+  async customFind() {
+    // ... do something
+  }
+}
diff --git a/core/dal-runtime/test/fixtures/modules/generate_codes_not_overwrite_dao/package.json b/core/dal-runtime/test/fixtures/modules/generate_codes_not_overwrite_dao/package.json
new file mode 100644
index 00000000..1769916d
--- /dev/null
+++ b/core/dal-runtime/test/fixtures/modules/generate_codes_not_overwrite_dao/package.json
@@ -0,0 +1,6 @@
+{
+  "name": "dal",
+  "eggModule": {
+    "name": "dal"
+  }
+}