四级联动下拉html代码：

<select id="Select1" name="Select1" autocomplete="off"></select>
<select id="Select2" name="Select2" autocomplete="off"></select>
<select id="Select3" name="Select3" autocomplete="off"></select>
<select id="Select4" name="Select4" autocomplete="off"></select>

定义四级联动下拉数据

var fourSelectData = {
    "省份": {val: "", items: {
            "城市": {val: "", items: {
                    "区县": {val: "", items: {
                            "乡镇": ""
                        }}
                }}
        }},
    "江苏": {val: "02", items: {
            "南京": {val: "0201", items: {
                    "玄武区": {val: "020101", items: {
                            "玄武区1": "02010101",
                            "玄武区2": "02010102",
                            "玄武区3": "02010103",
                            "玄武区4": "02010104",
                        }}
                }},
            "盐城": {val: "0202", items: {
                    "阜宁县": {val: "020201", items: {
                            "阜城镇": "02020101",
                            "三灶镇": "02020102",
                            "陈良镇": "02020103",
                            "郭墅镇": "02020103",
                        }},
                    "滨海县": {val: "020202", items: {
                            "通榆镇": "02020201",
                            "蔡桥镇": "02020202"
                        }}
                }}
        }},
};

初始化数据并调用数据

var defaults = {
    s1: 'Select1',
    s2: 'Select2',
    s3: 'Select3',
    s4: 'Select4',
    v1: "02",
    v2: "0202",
    v3: "020202",
    v4: "02020202"
};
$(function() {
    fourSelect(defaults);
});