diff --git a/.changelog/3560.txt b/.changelog/3560.txt
new file mode 100644
index 0000000000..284313fba0
--- /dev/null
+++ b/.changelog/3560.txt
@@ -0,0 +1,3 @@
+```release-note:enhancement
+resource/tencentcloud_mysql_readonly_instance: optmize code logic
+```
diff --git a/tencentcloud/services/cdb/resource_tc_mysql_instance.go b/tencentcloud/services/cdb/resource_tc_mysql_instance.go
index 8c7c16090b..16979e5e5c 100644
--- a/tencentcloud/services/cdb/resource_tc_mysql_instance.go
+++ b/tencentcloud/services/cdb/resource_tc_mysql_instance.go
@@ -182,6 +182,7 @@ func TencentMsyqlBasicInfo() map[string]*schema.Schema {
 		"cluster_topology": {
 			Type:        schema.TypeList,
 			Optional:    true,
+			Computed:    true,
 			MaxItems:    1,
 			Description: "Cluster Edition node topology configuration. Note: If you purchased a cluster edition instance, this parameter is required. You need to set the RW and RO node topology of the cluster edition instance. The RO node range is 1-5. Please set at least 1 RO node.",
 			Elem: &schema.Resource{
@@ -325,7 +326,7 @@ func ResourceTencentCloudMysqlInstance() *schema.Resource {
 			Optional:     true,
 			ValidateFunc: tccommon.ValidateAllowedIntValue([]int{0, 1}),
 			Default:      0,
-			Description:  "Availability zone deployment method. Available values: 0 - Single availability zone; 1 - Multiple availability zones.",
+			Description:  "Availability zone deployment method. Available values: 0 - Single availability zone; 1 - Multiple availability zones. Readonly instance settings are not supported.",
 		},
 		"first_slave_zone": {
 			Type:        schema.TypeString,
diff --git a/tencentcloud/services/cdb/resource_tc_mysql_readonly_instance.go b/tencentcloud/services/cdb/resource_tc_mysql_readonly_instance.go
index 9f941a2444..3b955bb90d 100644
--- a/tencentcloud/services/cdb/resource_tc_mysql_readonly_instance.go
+++ b/tencentcloud/services/cdb/resource_tc_mysql_readonly_instance.go
@@ -64,8 +64,9 @@ func ResourceTencentCloudMysqlReadonlyInstance() *schema.Resource {
 
 		Importer: &schema.ResourceImporter{
 			State: helper.ImportWithDefaultValue(map[string]interface{}{
-				"prepaid_period": 1,
-				"force_delete":   false,
+				"prepaid_period":    1,
+				"force_delete":      false,
+				"slave_deploy_mode": 0,
 			}),
 		},
 		Schema: readonlyInstanceInfo,
@@ -410,6 +411,9 @@ func resourceTencentCloudMysqlReadonlyInstanceRead(d *schema.ResourceData, meta
 		_ = d.Set("ro_group_id", *roGroup.RoGroupId)
 	}
 
+	// set no used fields to default value to fix diff
+	_ = d.Set("slave_deploy_mode", 0)
+
 	return nil
 }
 
diff --git a/website/docs/r/mysql_instance.html.markdown b/website/docs/r/mysql_instance.html.markdown
index 43ae3c9c8e..5c9d58c6d2 100644
--- a/website/docs/r/mysql_instance.html.markdown
+++ b/website/docs/r/mysql_instance.html.markdown
@@ -233,7 +233,7 @@ If it is not specified, it defaults to a universal instance.
 * `root_password` - (Optional, String) Password of root account. This parameter can be specified when you purchase master instances, but it should be ignored when you purchase read-only instances or disaster recovery instances.
 * `second_slave_zone` - (Optional, String) Zone information about second slave instance.
 * `security_groups` - (Optional, Set: [`String`]) Security groups to use.
-* `slave_deploy_mode` - (Optional, Int) Availability zone deployment method. Available values: 0 - Single availability zone; 1 - Multiple availability zones.
+* `slave_deploy_mode` - (Optional, Int) Availability zone deployment method. Available values: 0 - Single availability zone; 1 - Multiple availability zones. Readonly instance settings are not supported.
 * `slave_sync_mode` - (Optional, Int) Data replication mode. 0 - Async replication; 1 - Semisync replication; 2 - Strongsync replication.
 * `subnet_id` - (Optional, String) Private network ID. If `vpc_id` is set, this value is required.
 * `tags` - (Optional, Map) Instance tags.