你可以试试这样
为计数器添加隐藏字段
<input type='hidden' id='counter' value ='0' />
点击事件的变化
$('.add_new').click(function (e) {
var count = parseInt($("#counter").val(),10);
$("#counter").val(count+1);
var cloneEle = $(this).prev(".sub_container").clone(true);
cloneEle.attr("class","sub_container"+count)
cloneEle.find("input[type='text']").val('');
cloneEle.find('input[type="submit"]').val("Submit");
cloneEle.find('input[type="submit"]').attr("id","btnSubmit"+count)
cloneEle.appendTo('.container');
$('.preview_message').last().html('');
$('.preview_name').last().html('');
});
jsfiddle 演示