diff --git a/src/apis/watch.ts b/src/apis/watch.ts
index ba431af5..8fe0c5af 100644
--- a/src/apis/watch.ts
+++ b/src/apis/watch.ts
@@ -1,6 +1,6 @@
 import { ComponentInstance } from '../component';
 import { Ref, isRef } from '../reactivity';
-import { assert, logError, noopFn } from '../utils';
+import { assert, logError, noopFn, warn } from '../utils';
 import { defineComponentInstance } from '../helper';
 import { getCurrentVM, getCurrentVue } from '../runtimeContext';
 import { WatcherPreFlushQueueKey, WatcherPostFlushQueueKey } from '../symbols';
@@ -54,6 +54,30 @@ function installWatchEnv(vm: any) {
   vm.$on('hook:updated', flushPostQueue);
 }
 
+function getWatcherOption(options?: Partial<WatcherOption>): WatcherOption {
+  return {
+    ...{
+      lazy: false,
+      deep: false,
+      flush: 'post',
+    },
+    ...options,
+  };
+}
+
+function getWatcherVM() {
+  let vm = getCurrentVM();
+  if (!vm) {
+    if (!fallbackVM) {
+      fallbackVM = defineComponentInstance(getCurrentVue());
+    }
+    vm = fallbackVM;
+  } else if (!hasWatchEnv(vm)) {
+    installWatchEnv(vm);
+  }
+  return vm;
+}
+
 function flushQueue(vm: any, key: any) {
   const queue = vm[key];
   for (let index = 0; index < queue.length; index++) {
@@ -222,6 +246,15 @@ function createWatcher(
   };
 }
 
+export function watchEffect(
+  effect: SimpleEffect,
+  options?: Omit<Partial<WatcherOption>, 'lazy'>
+): StopHandle {
+  const opts = getWatcherOption(options);
+  const vm = getWatcherVM();
+  return createWatcher(vm, effect, null, opts);
+}
+
 export function watch<T = any>(
   source: SimpleEffect,
   options?: Omit<Partial<WatcherOption>, 'lazy'>
@@ -247,27 +280,19 @@ export function watch(
     callback = cb as WatcherCallBack<unknown>;
   } else {
     // effect watch
+    if (process.env.NODE_ENV !== 'production') {
+      warn(
+        `\`watch(fn, options?)\` signature has been moved to a separate API. ` +
+          `Use \`watchEffect(fn, options?)\` instead. \`watch\` now only ` +
+          `supports \`watch(source, cb, options?) signature.`
+      );
+    }
     options = cb as Partial<WatcherOption>;
     callback = null;
   }
 
-  const opts: WatcherOption = {
-    ...{
-      lazy: false,
-      deep: false,
-      flush: 'post',
-    },
-    ...options,
-  };
-  let vm = getCurrentVM();
-  if (!vm) {
-    if (!fallbackVM) {
-      fallbackVM = defineComponentInstance(getCurrentVue());
-    }
-    vm = fallbackVM;
-  } else if (!hasWatchEnv(vm)) {
-    installWatchEnv(vm);
-  }
+  const opts = getWatcherOption(options);
+  const vm = getWatcherVM();
 
   return createWatcher(vm, source, callback, opts);
 }
diff --git a/test/apis/watch.spec.js b/test/apis/watch.spec.js
index 696edc1e..cbe3f439 100644
--- a/test/apis/watch.spec.js
+++ b/test/apis/watch.spec.js
@@ -1,5 +1,5 @@
 const Vue = require('vue/dist/vue.common.js');
-const { ref, reactive, watch } = require('../../src');
+const { ref, reactive, watch, watchEffect } = require('../../src');
 
 describe('api/watch', () => {
   const anyFn = expect.any(Function);
@@ -298,11 +298,11 @@ describe('api/watch', () => {
         const x = ref(0);
 
         // prettier-ignore
-        watch(() => { void x.value; result.push('sync getter'); }, { flush: 'sync' });
+        watchEffect(() => { void x.value; result.push('sync effect'); }, { flush: 'sync' });
         // prettier-ignore
-        watch(() => { void x.value; result.push('pre getter'); }, { flush: 'pre' });
+        watchEffect(() => { void x.value; result.push('pre effect'); }, { flush: 'pre' });
         // prettier-ignore
-        watch(() => { void x.value; result.push('post getter'); }, { flush: 'post' });
+        watchEffect(() => { void x.value; result.push('post effect'); }, { flush: 'post' });
 
         // prettier-ignore
         watch(x, () => { result.push('sync callback') }, { flush: 'sync' })
@@ -321,11 +321,11 @@ describe('api/watch', () => {
       },
       template: `<div>{{x}}</div>`,
     }).$mount();
-    expect(result).toEqual(['sync getter', 'sync callback', 'pre callback', 'post callback']);
+    expect(result).toEqual(['sync effect', 'sync callback', 'pre callback', 'post callback']);
     result.length = 0;
 
     waitForUpdate(() => {
-      expect(result).toEqual(['pre getter', 'post getter']);
+      expect(result).toEqual(['pre effect', 'post effect']);
       result.length = 0;
 
       vm.inc();
@@ -333,12 +333,12 @@ describe('api/watch', () => {
       .then(() => {
         expect(result).toEqual([
           'before inc',
-          'sync getter',
+          'sync effect',
           'sync callback',
           'after inc',
-          'pre getter',
+          'pre effect',
           'pre callback',
-          'post getter',
+          'post effect',
           'post callback',
         ]);
       })
@@ -352,7 +352,7 @@ describe('api/watch', () => {
       const vm = new Vue({
         setup() {
           const count = ref(0);
-          watch(_onCleanup => {
+          watchEffect(_onCleanup => {
             onCleanup = _onCleanup;
             spy(count.value);
             renderedText = vm.$el.textContent;
@@ -384,7 +384,7 @@ describe('api/watch', () => {
       const vm = new Vue({
         setup() {
           const count = ref(0);
-          watch(
+          watchEffect(
             () => {
               spy(count.value);
             },
@@ -563,7 +563,7 @@ describe('api/watch', () => {
 
     it('simple effect', done => {
       const obj = reactive({ a: 1 });
-      watch(() => spy(obj.a));
+      watchEffect(() => spy(obj.a));
       expect(spy).not.toHaveBeenCalled();
       waitForUpdate(() => {
         expect(spy).toBeCalledTimes(1);
@@ -596,10 +596,10 @@ describe('api/watch', () => {
       return p;
     }
 
-    it('work with (single getter)', done => {
+    it('work with effect', done => {
       const id = ref(1);
       const promises = [];
-      watch(onCleanup => {
+      watchEffect(onCleanup => {
         const val = getAsyncValue(id.value);
         promises.push(val);
         onCleanup(() => {
@@ -617,10 +617,10 @@ describe('api/watch', () => {
         .then(done);
     });
 
-    it('run cleanup when watch stops (single getter)', done => {
+    it('run cleanup when watch stops (effect)', done => {
       const spy = jest.fn();
       const cleanup = jest.fn();
-      const stop = watch(onCleanup => {
+      const stop = watchEffect(onCleanup => {
         spy();
         onCleanup(cleanup);
       });
@@ -651,7 +651,7 @@ describe('api/watch', () => {
     it('should not collect reactive in onCleanup', done => {
       const ref1 = ref(1);
       const ref2 = ref(1);
-      watch(onCleanup => {
+      watchEffect(onCleanup => {
         spy(ref1.value);
         onCleanup(() => {
           ref2.value = ref2.value + 1;
diff --git a/test/templateRefs.spec.js b/test/templateRefs.spec.js
index 27373a22..260e9d4d 100644
--- a/test/templateRefs.spec.js
+++ b/test/templateRefs.spec.js
@@ -1,5 +1,5 @@
 const Vue = require('vue/dist/vue.common.js');
-const { ref, watch, createElement: h } = require('../src');
+const { ref, watchEffect, createElement: h } = require('../src');
 
 describe('ref', () => {
   it('should work', done => {
@@ -7,7 +7,7 @@ describe('ref', () => {
     const vm = new Vue({
       setup() {
         const ref1 = ref(null);
-        watch(() => {
+        watchEffect(() => {
           dummy = ref1.value;
         });
 
@@ -35,7 +35,7 @@ describe('ref', () => {
       setup() {
         const ref1 = ref(null);
         const ref2 = ref(null);
-        watch(() => {
+        watchEffect(() => {
           dummy1 = ref1.value;
           dummy2 = ref2.value;
         });