"gradeId" : {
required : true,
min : 0,
remote: {
url: "gradeManager-checkGrade.action",
type: "post",
dataType: "json",
data: {
'gradeId' : function() {
return $("#gradeId").val();
},
'schoolId' : function() {
return $("#schoolId").val();
}
}
}
}

<div class="control-group">
<label class="control-label" for="schoolId">學校</label>
<div class="controls">
<s:select name="schoolId" list="schools" listKey="schoolId"
listValue="schoolName" headerKey="-1" headerValue="請選擇學校"></s:select>
</div>
</div>

<div class="control-group">
<label class="control-label" for="gradeId">年級</label>
<div class="controls">
<s:select name="gradeId" list="grades" listKey="gradeId"
listValue="gradeName" headerKey="-1" headerValue="請選擇年級"></s:select>
</div>
</div>

$("#schoolId").change(function(){
$("#gradeId").removeData("previousValue");
});