< script type="text/vbs">
dim menu(9)
menu(0)="<select><option value='1'>1</option><option value='2'>2</option><option value='3'>3</option></select>"
menu(1)="<select><option value='4'>4</option><option value='5'>5</option><option value='6'>6</option></select>"
menu(2)="<select><option value='7'>7</otpion><option value='8'>8</otpion><option value='9'>9</option></select>"
menu(3)="<select><option value='0'>0</otpion><option value='11'>11</otpion><option value='12'>12</option></select>"
</script>

<select id="big_class" onchange="class_menu.innerHTML=menu(big_class.selectedIndex)">
<option>0</option>
<option>1</option>
<option>2</option>
<option>3</option>
<option>4</option>
<option>5</option>
</select>

<span id="class_menu"></span>
</BODY >

另一种方法

<select id="a" onchange="change(this.selectedIndex)">
<option>1</option>
<option>2</option>
</select>
<select id="b"/>
< script>
var data = [
["J","a","v","a"],
["s","c","r","i","p","t"]
];
function change(x){
 var s = data[x];
 with(document.getElementById("b")) {
  length = 0;
  for (var i=0;i<s.length;i++)
   options[length] = new Option(s[i],s[i]);
 }
}
change(0);
</script >