diff --git a/packages/reactivity/src/effect.ts b/packages/reactivity/src/effect.ts
index bf3a5fd..9f30aa9 100644
--- a/packages/reactivity/src/effect.ts
+++ b/packages/reactivity/src/effect.ts
@@ -41,6 +41,7 @@ export class ReactiveEffect<T = any> {
     activeEffect = this
     return this.fn() //完成第一次getter行为的触发
   }
+  stop() {}
 }
 
 /**
diff --git a/packages/reactivity/src/index.ts b/packages/reactivity/src/index.ts
index 7964e45..0ce2c70 100644
--- a/packages/reactivity/src/index.ts
+++ b/packages/reactivity/src/index.ts
@@ -1,4 +1,4 @@
-export { reactive } from './reactive'
-export { effect } from './effect'
+export { reactive, isReactive } from './reactive'
+export { effect, ReactiveEffect } from './effect'
 export { ref } from './ref'
 export { computed } from './computed'
diff --git a/packages/reactivity/src/reactive.ts b/packages/reactivity/src/reactive.ts
index 2ed7ec0..e585f1e 100644
--- a/packages/reactivity/src/reactive.ts
+++ b/packages/reactivity/src/reactive.ts
@@ -8,6 +8,10 @@ import { isObject } from '@vue/shared'
  */
 export const reactiveMap = new WeakMap<object, any>()
 
+export const enum ReactiveFlags {
+  IS_REACTIVE = '__v_isReactive'
+}
+
 /**
  * 为复杂数据类型, 创建响应式对象
  * @param target 被代理的对象
@@ -35,7 +39,8 @@ function createReactiveObject(
   }
   //未被代理则生成proxy实例
   const proxy = new Proxy(target, baseHandlers)
-
+  //添加reactive标识
+  proxy[ReactiveFlags.IS_REACTIVE] = true
   //缓存代理对象
   proxyMap.set(target, proxy)
   return proxy
@@ -43,3 +48,7 @@ function createReactiveObject(
 
 export const toReactive = <T extends unknown>(value: T): T =>
   isObject(value) ? reactive(value as object) : value
+
+export function isReactive(value): boolean {
+  return !!(value && value[ReactiveFlags.IS_REACTIVE])
+}
diff --git a/packages/runtime-core/src/apiWatch.ts b/packages/runtime-core/src/apiWatch.ts
new file mode 100644
index 0000000..7a5e5c4
--- /dev/null
+++ b/packages/runtime-core/src/apiWatch.ts
@@ -0,0 +1,60 @@
+import { EMPTY_OBJ, hasChanged } from '@vue/shared'
+import { isReactive, ReactiveEffect } from '@vue/reactivity'
+import { queuePreFlushCb } from '@vue/runtime-core'
+
+export interface WatchOptions<immediate = boolean> {
+  immediate?: immediate
+  deep?: boolean
+}
+
+export function watch(source, cb: Function, options?: WatchOptions) {
+  return doWatch(source, cb, options)
+}
+
+function doWatch(
+  source,
+  cb: Function,
+  { immediate, deep }: WatchOptions = EMPTY_OBJ
+) {
+  let getter: () => any
+  if (isReactive(source)) {
+    getter = () => source
+    deep = true
+  } else {
+    getter = () => {}
+  }
+  //处理deep的状态
+  if (cb && deep) {
+    //todo
+    //浅拷贝的形式--指向同样的内存空间
+    const baseGetter = getter
+    getter = () => baseGetter()
+  }
+
+  let oldValue = {}
+  //每次执行等同于watch被触发一次
+  const job = () => {
+    if (cb) {
+      const newValue = effect.run()
+      if (deep || hasChanged(newValue, oldValue)) {
+        cb(newValue, oldValue)
+        oldValue = newValue
+      }
+    }
+  }
+  //调度器
+  let scheduler = () => queuePreFlushCb(job)
+  const effect = new ReactiveEffect(getter, scheduler)
+  if (cb) {
+    if (immediate) {
+      job()
+    } else {
+      oldValue = effect.run()
+    }
+  } else {
+    effect.run()
+  }
+  return () => {
+    effect.stop()
+  }
+}
diff --git a/packages/runtime-core/src/index.ts b/packages/runtime-core/src/index.ts
index a3a2657..c1885a8 100644
--- a/packages/runtime-core/src/index.ts
+++ b/packages/runtime-core/src/index.ts
@@ -1 +1,2 @@
 export { queuePreFlushCb } from './scheduler'
+export { watch } from './apiWatch'
diff --git a/packages/shared/src/index.ts b/packages/shared/src/index.ts
index 5494e3b..f740520 100644
--- a/packages/shared/src/index.ts
+++ b/packages/shared/src/index.ts
@@ -15,3 +15,5 @@ export const isFunction = (val: unknown): val is Function => {
 }
 
 export const extend = Object.assign
+
+export const EMPTY_OBJ: { readonly [key: string]: any } = {}
diff --git a/packages/vue/examples/reactivity/watch.html b/packages/vue/examples/reactivity/watch.html
new file mode 100644
index 0000000..1340c0f
--- /dev/null
+++ b/packages/vue/examples/reactivity/watch.html
@@ -0,0 +1,26 @@
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>Document</title>
+  <script src="../../dist/vue.js"></script>
+</head>
+<body>
+<div id="app"></div>
+</body>
+<script>
+  const { reactive,watch } = Vue
+  const obj=reactive({
+    name:'张三'
+  })
+
+  watch(obj,(value,oldValue)=>{
+    console.log('watch 监听被触发---value',value);
+  },{
+    immediate:true
+  })
+  setTimeout(()=>{
+    obj.name='李四'
+  },2000)
+</script>
+</html>
\ No newline at end of file
diff --git a/packages/vue/src/index.ts b/packages/vue/src/index.ts
index 8fb36c5..08ac420 100644
--- a/packages/vue/src/index.ts
+++ b/packages/vue/src/index.ts
@@ -1,2 +1,2 @@
 export { reactive, effect, ref, computed } from '@vue/reactivity'
-export { queuePreFlushCb } from '@vue/runtime-core'
+export { queuePreFlushCb, watch } from '@vue/runtime-core'