<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script>
function ds(){
var a = document.getElementById('ddd');
a.checked = true;
var b = document.getElementById('sss');
b.click();
}
</script>
</head>
<body>
<a href="#" onclick = "ds();">Кликни</a><br>
<input id="ddd" type="checkbox"/>
<input type="button" id="sss" onclick="alert('кликнулось');" value="кнопка"/>
</body>
</html>