<div id="menuContainer">

  <div id="menu">

    <ul>

      <li>menu1</li>

      <li>menu2</li>

    </ul>

  </div>

  <div> ...長內容.... </div>

</div>

        var __ContainerHeight = 5000;

        var __ContainerTop = 160;

        var __MenuHeight = 550;

        var __FixedTop = 20;



        $(window).load(function () {



            __ContainerHeight = $("#menuContainer").height();

            __ContainerTop = $("#menuContainer").offset().top;

            __MenuHeight = $("#menu").height();



            $("#menu").css({ "top": __FixedTop + "px", "position": "absolute" });

            $(window).scroll(function () {

                var scrolls = $(this).scrollTop();

                //console.log(scrolls);

                if (scrolls < __ContainerTop) {

                    $("#menu").css({ "top": __FixedTop + "px", "position": "absolute" });

                }

                else if ((scrolls + __MenuHeight + __FixedTop) > (__ContainerHeight + __ContainerTop)) {

                    $("#menu").css({ "top": (__ContainerHeight - __MenuHeight) + "px", "position": "absolute" });

                }

                else {

                    $("#menu").css({ "top": __FixedTop + "px", "position": "fixed" });

                }

            });



        });