试试：

var men = '<option selected="selected" value=""> Choose Size </option><option value="36">36</option><option value="38">38</option><option value="40">40</option>';
var women = '<option selected="selected" value=""> Choose Size </option><option value="30">30</option><option value="29">29</option><option value="28">28</option>';
var children = '<option selected="selected" value=""> Choose Size </option><option value="12">12</option><option value="11">11</option><option value="10">10</option>';
$(document).ready(function(){
    $("select#select_1").on('change',function(){
        if($(this).val()=="Mens Suits"){
            $("select#select_3").html(men);
        }else if($(this).val()=="Womens Suit"){
            $("select#select_3").html(women);
        }else if($(this).val()=="Children Suit"){
            $("select#select_3").html(children);
        }
    });
});

DEMO FIDDLE