i found solution:-
We should bind attribute "hiddenvalue" the it will be bind with server side value
and it will be found client side like
item.Attributes.Add("hiddenValue", item.Value);
$("#<%= CheckBoxList1.ClientID %> input:checkbox:checked").each(function() {
var label = $('label[for=' + this.id + ']').html();
var value = $(this).parent().attr('hiddenValue');
labels += label + ", ";
values += value + ", ";
});