很简单的思路，通过三个鼠标事件：点击、移动、抬起，只要计算出当前位置即可，如果是图片的话加入：e.preventDefault();即可
<!DOCTYPE html>
<html>
<head>
<title>鼠标拖动</title>
<style type="text/css">
#dv {
width: 100px;
height: 100px;
background-color: blue;
border-radius: 50%;
position: absolute;
}
</style>
</head>
<body>
<div id="dv"></div>
</body>
<script type="text/javascript">
//获取元素
var dv = document.getElementById('dv');
var x = 0;
var y = 0;
var l = 0;
var t = 0;
var isDown = false;
//鼠标按下事件
dv.onmousedown = function(e) {
//获取x坐标和y坐标
x = e.clientX;
y = e.clientY;
//获取左部和顶部的偏移量
l = dv.offsetLeft;
t = dv.offsetTop;
//开关打开
isDown = true;
//设置样式
dv.style.cursor = 'move';
}
//鼠标移动
window.onmousemove = function(e) {
if (isDown == false) {
return;
}
//获取x和y
var nx = e.clientX;
var ny = e.clientY;
//计算移动后的左偏移量和顶部的偏移量
var nl = nx - (x - l);
var nt = ny - (y - t);
dv.style.left = nl + 'px';
dv.style.top = nt + 'px';
}
//鼠标抬起事件
dv.onmouseup = function() {
//开关关闭
isDown = false;
dv.style.cursor = 'default';
}
</script>
</html>