Once i click on label select button should get open

Do you want to do something like this? http://jsfiddle.net/Yh3Jf/6/

    <label id="l">sachin</label>
    <select id="s">
        <option>1</option>
        <option>2</option>        
        <option>3</option>
        <option>4</option>
   </select>  

$("#l").click(function () {
    var size = $('#s option').size();
    if (size != $("#s").prop('size')) {
        $("#s").prop('size', size);
    } else {
        $("#s").prop('size', 1);
    }
})

No need for javascript here, just style it with CSS and use pointer events :

<label>
<select>
   <option value="0">Zero</option>
   <option value="1">One</option>
</select>
</label>

and the relative CSS is

label:after {
    content:'\25BC';
    display:inline-block;
    color:#000;
    background-color:#fff;
    margin-left:-17px;   /* remove the damn :after space */
    pointer-events:none; /* let the click pass trough */
}

Here is a ugly fiddle sample: https://jsfiddle.net/1rofzz89/

Wrong guys; to get the native selection-list just make a invisible clone under the mouse:

$("label").mouseover(function(){
    var $this = $(this);
    var $input = $('#' + $(this).attr('for')); 
    if ($input.is("select") && !$('.lfClon').length) {
        var $clon = $input.clone();
        var getRules = function($ele){ return {
            position: 'absolute',
            left: $ele.offset().left,
            top: $ele.offset().top,
            width: $ele.outerWidth(),
            height: $ele.outerHeight(),
            opacity: 0,
            margin: 0,
            padding: 0
        };};
        var rules = getRules($this);
        $clon.css(rules);
        $clon.on("mousedown.lf", function(){
            $clon.css({
                marginLeft: $input.offset().left - rules.left,
                marginTop: $input.offset().top - rules.top,
            });
            $clon.on('change blur', function(){
                $input.val($clon.val()).show();
                $clon.remove();
            });
            $clon.off('.lf');
        });
        $clon.on("mouseout.lf", function(){
            $(this).remove();
        });
        $clon.prop({id:'',className:'lfClon'});
        $clon.appendTo('body');
    }
});

Tested on IE10, Chrome 27 and Firefox 22

Demo: http://jsfiddle.net/Yh3Jf/24/