index.php页面程序：

<?php
header("Content-type: text/html; charset=gb2312");
$mypdo=new pdo("mysql:host=localhost;dbname=news","root","");
$sql="selects * from newstype";
$mypdo->query("set names gb2312");
$stmt=$mypdo->query($sql);
$rows=$stmt->fetchAll(PDO::FETCH_ASSOC);
?>

<script src="jquery-1.11.2.min.js"></script>

<script type="text/javascript">
$(function(){
 $("#menu1").change(function(){
  $.getJSON("view.php",{index:$(this).val()},function(data){
     var xs="";
     var xx="";
     for(var i=0;i<=data.length;i++){
      xx+="<option value='"+data[i].id+"'>"+data[i].shi+"</option>";
      //xx+=data[i].id+data[i].shi;
      $("#shi").html(xx);
     }
   });
 })
 
 $("#menu1").change();
})
</script>

<table width="900" border="0" cellspacing="0" cellpadding="0">
  <tr>
    <td width="120">
    <select id="menu1">
    <?php foreach($rows as $rs){?>
    <option value="<?php echo $rs['typeid'] ?>"><?php echo $rs['typename'] ?></option>
    <?php } ?>
    </select></td>
    <td width="120"><select id="shi"><option>未选择</option></select></td>
    <td>&nbsp;</td>
  </tr>
</table>

view.php提供json格式数据：

<?php
header("Content-type: text/html; charset=gb2312");

if(!isset($_GET['index'])){
 $tid=3;
}
else{
 $tid=$_GET['index'];
}
$mypdo=new pdo("mysql:host=localhost;dbname=news","root","");
$sql="selects * from detailtype where typeid=$tid";
$mypdo->query("set names gb2312");
$stmt=$mypdo->query($sql);
$rows=$stmt->fetchAll(PDO::FETCH_ASSOC);
$JSON_text="[";

$s=count($rows);
$i=1;
foreach($rows as $rs){
 $JSON_text.='{"id":'.$rs['detailid'].',"shi":"'.$rs['detailname'].'"}';
 if($i<$s){
  $JSON_text=$JSON_text.",";
 }
 $i=$i+1;
}

$JSON_text.="]";
echo $JSON_text;
?>