<body>
<input type="checkbox" id="ckAll" />check all<br />
<input type="checkbox" name="sub" />1<br />
<input type="checkbox" name="sub"/>2<br />
<input type="checkbox" name="sub"/>3<br />
<input type="checkbox" name="sub"/>4<br />
<script>
$("#ckAll").click(function() {
$("input[name='sub']").prop("checked", this.checked);
});
$("input[name='sub']").click(function() {
var $subs = $("input[name='sub']");
$("#ckAll").prop("checked" , $subs.length == $subs.filter(":checked").length ? true :false);
});
</script>
</body>