$(window).scroll(function(){

    var scrollpos   = $(this).scrollTop();
    var pad         = $('.panel_header').outerHeight();

    $('.form_group').not('.sub_group').each(function(i){

        if(scrollpos + $(window).height() == $(document).height()){

            $('ul.tabs li').removeClass('active_tab');
            $('ul.tabs li:last-child').addClass('active_tab');

            return false;

        } else if(scrollpos+pad < $(this).position().top+($(this).height()/2)){

            var id  = $(this).attr('id').replace('-table','-tab');
            var tab = $('#'+id);

            if(tab.length > 0){

                $('ul.tabs li').removeClass('active_tab');
                tab.addClass('active_tab');
            }
            return false;
        }
    });
});

解决方法

var ScrollSpy = function() {

  var pad = 10;
  var offsets = [];
  var targets = [];
  var activeTarget = null;
  
  function init() {      
    $(document.body).find(".form_group").not(".sub_group").map(function () {    
      var $el   = $(this);
      var id  = $(this).attr('id').replace('-table','-tab');
      var $li = $('#'+id);
      
      return  [[$el.offset().top,$li[0]]];
    }).sort(function (a,b) { return a[0] - b[0] }).each(function () {
      offsets.push(this[0])
      targets.push(this[1])
    });
  };
  
  function activate(target) {
  	activeTarget = target;
    clear();
  	$(target).addClass('active_tab');
  };
  
  function clear() {
    $('ul.tabs li').removeClass('active_tab'); 
  };
  
  function getScrollHeight() {
    return window.scrollHeight || Math.max(document.body.scrollHeight,document.documentElement.scrollHeight);
  };
  
  function spy()  {  
    var scrollTop = $(window).scrollTop() + pad;
    var scrollHeight = getScrollHeight();
    var maxScroll = pad + scrollHeight - $(window).height();
    
    if (scrollTop >= maxScroll) {
      return activeTarget != (i = targets[targets.length - 1]) && activate(i);
    }
    
    if (activeTarget && scrollTop < offsets[0]) {
      activeTarget = null;
      return clear();
    }
    
		for (i = offsets.length; i--;) {
      activeTarget != targets[i]
        && scrollTop >= offsets[i]
        && (offsets[i + 1] === undefined || scrollTop < offsets[i + 1])
        && activate(targets[i]);
    }
  };
  
  $(window).scroll(spy);
  init();
  spy();
};

jQuery(function($) {
	ScrollSpy();
});

body,html {
  padding:0;
  margin:0;
  position: relative;
}
.panel_header {
  background-color:#ccc;
  padding:5px;
}

.tabs {
  padding:0;
  list-style:none;
  position:fixed;
  margin-left:-125px;
  left:50%;
  top:10px;
}
.tabs li {
  float:left;
  margin-left:4px;
}
.tabs li a {
  padding:4px 10px;
  background-color:white;
  border:1px solid #ccc;
}
.tabs li.active_tab a {
  background-color:red;
}

.form_group {
  border:1px solid #ccc;
  min-height:500px;
  padding:10px;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<header style="height:120px"></header>
<ul class="tabs">
  <li id="1-tab"><a href="#">Tab 1</a></li>
  <li id="2-tab"><a href="#">Tab 2</a></li>
  <li id="3-tab"><a href="#">Tab 3</a></li>
  <li id="4-tab"><a href="#">Tab 4</a></li>
</ul>

<div class="form_group" id="1-table">
  <h3 class="panel_header">Form_group 1 </h3>
  <p>Sodales velit. Aliquam libero duis duis nam,pariatur etiam neque ridiculus nisl libero,quis dis enim. Justo natoque,suscipit quam leo elit mauris tortor venenatis,morbi libero magna lorem enim. Sociis sed eu auctor inceptos nec,commodo quis nostra pretium turpis,semper sapien amet pretium aliquam,mauris faucibus euismod. Sed justo odio justo aliquet,natoque duis,tristique ultricies eget sodales tempus vitae.</p>
  
</div>
<div class="form_group" id="2-table">
  <h3 class="panel_header">Form_group 2 </h3>
  <p>Sodales velit. Aliquam libero duis duis nam,tristique ultricies eget sodales tempus vitae.</p>
</div>
<div class="form_group" id="3-table">
  <h3 class="panel_header">Form_group 3 </h3>
  <p>Sodales velit. Aliquam libero duis duis nam,tristique ultricies eget sodales tempus vitae.</p>
</div>
<div class="form_group" id="4-table">
  <h3 class="panel_header">Form_group 4 </h3>
  <p>Sodales velit. Aliquam libero duis duis nam,tristique ultricies eget sodales tempus vitae.</p>
</div>

为了获得更好的体验,请以完整页面模式运行代码段.