var radios = document.YourFormName.YourRadioName;
var value;
for (var i=0; i < radios.length; i++)
if (radios[i].checked)
value = radios[i].value;alert(value);
var value;
for (var i=0; i < radios.length; i++)
if (radios[i].checked)
value = radios[i].value;alert(value);
<head>
<script language="javascript">
function chk() {
var i = parseInt(document.form1.text1.value, 10);
document.form1.radio1[i].checked = true;
}
</script>
</head>
<body>
<form name="form1">
<input type="radio" name="radio1">radio test 0<br>
<input type="radio" name="radio1">radio test 1</br>
输入你想选择的radio(从0开始)
<input type="text" name="text1" value=""><br>
<input type="button" value="select" onclick="chk()">
</form>
</body>
</html>