<!DOCTYPE html>

<html>

<head lang="en">

    <meta charset="UTF-8">

    <title></title>

    <style>

        *{margin: 0; padding: 0}

        #div1{width: 100px; height: 100px; background: red; position: absolute; left: 100px;

            top: 100px;}

    </style>

    <script src="jquery-1.12.3.min.js"></script>

    <script>

        $(function(){

            var disX = 0;

            var disY = 0;

            var $div1 = $("#div1");

            $div1.on('mousedown',function(ev){

                disX = ev.pageX - $(this).offset().left;

                disY = ev.pageY - $(this).offset().top;

                $(document).on('mousemove',function(ev){//此处忘了加ev, 找了一个多小时!

                    var left = ev.pageX - disX;

                    var top = ev.pageY - disY;

                    console.log(left+":"+top)

                    $div1.css('left',left);

                    $div1.css('top',top );

                });

                $(document).on('mouseup',function(){

                    console.log("off")

                    $(this).off();

                });

                return false;//按下的时候阻止默认事件

            })

        });

    </script>

</head>

<body style="height: 2000px">

    <div id="div1">divdiv</div>

</body>

</html>