根据参数显示类别（三级联动，需要JSON数据）

Scripts/Category.js

调用方法：

$(function () {
    BindCategory();
    //默认绑定文本框中的值
    BindCategoryData($("#txtCategoryId").val());
})

绑定三级联动（详情见：http://www.cnblogs.com/haozhenjie819/p/3887279.html）

function BindCategory() {
    var $txtCategory = $("#txtCategoryId");
    var _selectId = ["selBigClass", "selSmallClass", "selThreeClass"];
    for (var i = 0; i < _selectId.length; i++) {
        var select = document.createElement("select");
        select.id = _selectId[i];
        select.name = _selectId[i];
        $txtCategory.parent().append(select);
    }
    var $selBigClass = $("#selBigClass");
    var $selSmallClass = $("#selSmallClass");
    var $selThreeClass = $("#selThreeClass");
    $selSmallClass.hide();
    $selThreeClass.hide();
    $.getJSON("/Scripts/CategoryJson.js", function (json) {
        var html = ['<option value="">请选择大类</option>'];
        for (var key in json) {
            if (json[key].pid == 0) {
                html.push('<option value="' + json[key].id + '">' + json[key].name + '</option>');
            }
        }
        //第一级类别
        $selBigClass.empty().append(html.join('')).change(function () {
            $txtCategory.val(this.value);
            $selThreeClass.hide();
            $selSmallClass.show();
            var html = ['<option value="">请选择小类</option>'];
            for (var data in json) {
                if (json[data].pid == $("#selBigClass").val()) {
                    html.push('<option value="' + json[data].id + '">' + json[data].name + '</option>');
                }
            }
            //第二级类别
            $selSmallClass.empty().append(html.join('')).change(function () {
                $txtCategory.val(this.value);               
                $selThreeClass.show();
                var html = ['<option value="">请选择小类</option>'];
                for (var data in json) {
                    if (json[data].pid == $selSmallClass.val()) {
                        html.push('<option value="' + json[data].id + '">' + json[data].name + '</option>');
                    }
                }
                //第三级类别
                $selThreeClass.empty().append(html.join('')).change(function () {
                    $txtCategory.val(this.value);
                });
                //如果不存在第三级类别则隐藏第三级类别控件
                if ($selThreeClass.get(0).options.length <= 1) {
                    $selThreeClass.hide();
                    return false;
                }
            });
            //如果不存在第二级类别则隐藏第二级类别控件
            if ($selSmallClass.get(0).options.length <= 1) {
                $selSmallClass.hide();
                return false;
            }
           
        });
    });
};

根据参数显示默认值

var setBigClassTime;
//绑定数据
function BindCategoryData(CategoryId) {
    if (document.getElementById("selBigClass") == null || document.getElementById("selBigClass").length <= 0)
        setBigClassTime = setTimeout("BindCategoryData('" + CategoryId + "')", 200);
    else
        clearTimeout(setBigClassTime);
    $.getJSON('/Scripts/CategoryJson.js', function (json) {
        for (var key in json) {
            if (json[key].id == CategoryId) {
                json[key].id = CategoryId;
                var str = json[key].itemvalue;
                var _p = str.split("|")[2];
                var _c = json[key].pid;
                if (_p == _c) {
                    if (_p != "") {
                        $("#selBigClass").val(_p).change();
                        $("#selSmallClass").val(CategoryId);
                    }
                    else {
                        $("#selBigClass").val(CategoryId);
                    }
                }
                else {
                    $("#selBigClass").val(_p).change();
                    $("#selSmallClass").val(_c).change();
                    $("#selThreeClass").val(CategoryId).change();
                }
            }
        }
    });
}

Scripts/CategoryJson.js（如何生成json数据详见：http://www.cnblogs.com/haozhenjie819/p/3601676.html）

[{ "id": 31, "name": "u65b0u95fbu4e2du5fc3", "pid": 0, "itemvalue": "|0|" },
{ "id": 59, "name": "u52a0u76dfu5408u4f5c", "pid": 0, "itemvalue": "|0|" },
{ "id": 65, "name": "u4ea7u54c1u670du52a1", "pid": 0, "itemvalue": "|0|" },



{ "id": 60, "name": "u52a0u76dfu987bu77e5", "pid": 59, "itemvalue": "|0|59|" },
{ "id": 61, "name": "u52a0u76dfu6d41u7a0b", "pid": 59, "itemvalue": "|0|59|" },
{ "id": 62, "name": "u52a0u76dfu533au57df", "pid": 59, "itemvalue": "|0|59|" },



{ "id": 70, "name": "u63a8u8350u670du52a1", "pid": 65, "itemvalue": "|0|65|" },
{ "id": 71, "name": "u8ba1u8d39u65b9u5f0f", "pid": 65, "itemvalue": "|0|65|" },
{ "id": 72, "name": "u7528u6237u987bu77e5", "pid": 65, "itemvalue": "|0|65|" },
{ "id": 73, "name": "u7981u5bc4u8303u56f4", "pid": 65, "itemvalue": "|0|65|" },
{ "id": 75, "name": "u666eu901au5febu9012", "pid": 70, "itemvalue": "|0|65|70|" },
{ "id": 76, "name": "u7279u79cdu5febu4ef6", "pid": 70, "itemvalue": "|0|65|70|" },
{ "id": 77, "name": "u9650u65f6u6d3eu9001", "pid": 70, "itemvalue": "|0|65|70|" },
{ "id": 78, "name": "u4ee3u6536u8d37u6b3e", "pid": 70, "itemvalue": "|0|65|70|" },
{ "id": 79, "name": "u4fddu4ef7u670du52a1", "pid": 70, "itemvalue": "|0|65|70|" }, 
{ "id": 80, "name": "u4ee3u7b7eu56deu5355", "pid": 70, "itemvalue": "|0|65|70|"}]

web页面（给hidden赋值，类别编号为75）

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>三级联动</title>
    <script src="/Scripts/jquery-1.4.1.min.js" type="text/javascript"></script>
    <script src="/Scripts/Category.js" type="text/javascript"></script>  
</head>
<body>
    <form id="form1" runat="server">   
         <table>
            <tr>
                <td >新闻类别：</td>
                <td > <input id="txtCategoryId" name="txtCategoryId" type="hidden" runat="server" value="75" /></td>
            </tr>    
        </table>
    </form>    
</body>
</html>

效果图

涉及的知识点：【JavaScript split() 方法】返回值是一个字符串数组。