直接上代碼！！！
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GBK" />
<meta name="viewport" content="initial-scale=1.0, user-scalable=no" />
<style type="text/css">
body, html{width: 100%;height: 100%;margin:0;font-family:"微軟雅黑";}
#allmap {width: 100%; height:500px; overflow: hidden;}
#result {width:100%;font-size:12px;}
dl,dt,dd,ul,li{
margin:0;
padding:0;
list-style:none;
}
p{font-size:12px;}
dt{
font-size:14px;
font-family:"微軟雅黑";
font-weight:bold;
border-bottom:1px dotted #000;
padding:5px 0 5px 5px;
margin:5px 0;
}
dd{
padding:5px 0 0 5px;
}
li{
line-height:28px;
}
</style>
<script type="text/javascript" src="http://api.map.baidu.com/api?v=2.0&ak=I456EKI94mIHnfe8qgwW0BE6"></script>
<!--加載鼠標繪製工具-->
<script type="text/javascript" src="http://api.map.baidu.com/library/DrawingManager/1.4/src/DrawingManager_min.js"></script>
<link rel="stylesheet" href="http://api.map.baidu.com/library/DrawingManager/1.4/src/DrawingManager_min.css" />
<!--加載檢索信息窗口-->
<script type="text/javascript" src="http://api.map.baidu.com/library/SearchInfoWindow/1.4/src/SearchInfoWindow_min.js"></script>
<link rel="stylesheet" href="http://api.map.baidu.com/library/SearchInfoWindow/1.4/src/SearchInfoWindow_min.css" />
<title>鼠標繪製工具</title>
</head>
<body>
<div id="allmap" style="overflow:hidden;zoom:1;position:relative;">
<div id="map" style="height:100%;-webkit-transition: all 0.5s ease-in-out;transition: all 0.5s ease-in-out;"></div>
</div>
<div id="result">
<input type="button" value="獲取繪製的覆蓋物個數" οnclick="alert(overlays.length)"/>
<input type="button" value="清除所有覆蓋物" οnclick="clearAll()"/>
</div>
<script type="text/javascript">
// 百度地圖API功能
var map = new BMap.Map('map');
var poi = new BMap.Point(116.307852,40.057031);
map.centerAndZoom(poi, 16);
map.enableScrollWheelZoom();
var overlays = [];
var overlaycomplete = function(e){
overlays.push(e.overlay);
};
var styleOptions = {
strokeColor:"red", //邊線顏色。
fillColor:"red", //填充顏色。當參數爲空時，圓形將沒有填充效果。
strokeWeight: 3, //邊線的寬度，以像素爲單位。
strokeOpacity: 0.8, //邊線透明度，取值範圍0 - 1。
fillOpacity: 0.6, //填充的透明度，取值範圍0 - 1。
strokeStyle: 'solid' //邊線的樣式，solid或dashed。
}
//實例化鼠標繪製工具
var drawingManager = new BMapLib.DrawingManager(map, {
isOpen: false, //是否開啓繪製模式
enableDrawingTool: true, //是否顯示工具欄
drawingToolOptions: {
anchor: BMAP_ANCHOR_TOP_RIGHT, //位置
offset: new BMap.Size(5, 5), //偏離值
},
circleOptions: styleOptions, //圓的樣式
polylineOptions: styleOptions, //線的樣式
polygonOptions: styleOptions, //多邊形的樣式
rectangleOptions: styleOptions //矩形的樣式
});
//添加鼠標繪製工具監聽事件，用於獲取繪製結果
drawingManager.addEventListener('overlaycomplete', overlaycomplete);
function clearAll() {
for(var i = 0; i < overlays.length; i++){
map.removeOverlay(overlays[i]);
}
overlays.length = 0
}
</script>
</body>
</html>