djamali,
<!DOCTYPE html>
<html lang="en">
<head>
<script src="http://code.jquery.com/jquery-1.11.1.js"></script>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<select id="1">
<option>qwewe</option>
<option>asdsda</option>
<option>zxcxzc</option>
</select>
<select id="2">
<option>asdsd</option>
<option>qweqwe</option>
<option>asdas</option>
</select>
<select id="3">
<option>sdsd</option>
<option>sadsa</option>
<option>asds</option>
</select>
<button onclick="changeLink()">Изменить адресс ссылки</button>
<a href="aaaaa">aaaaaa</a>
</body>
</html>
<script>
function changeLink(){
var part1 = $('#1').val();
var part2 = $('#2').val();
var part3 = $('#3').val();
link = part1+"&"+part2+/*Для рони=)))*/"&"+part3;
$('a').attr('href', link);
$('a').html(link);
}
</script>