<!-- Latest compiled and minified CSS -->
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.10.0/css/bootstrap-select.min.css">

<!-- Latest compiled and minified JavaScript -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.10.0/js/bootstrap-select.min.js"></script>

<!-- (Optional) Latest compiled and minified JavaScript translation files -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.10.0/js/i18n/defaults-*.min.js"></script>

<div class="form-group">
    <label class="col-sm-3 control-label">客资类型：</label>
    <div class="col-sm-4">
    <select id="usertype" name="usertype" class="selectpicker show-tick form-control" multiple data-live-search="false">
     <option value="0">苹果</option>
     <option value="1">菠萝</option>
     <option value="2">香蕉</option>
     <option value="3">火龙果</option>
     <option value="4">梨子</option>
     <option value="5">草莓</option>
     <option value="6">哈密瓜</option>
     <option value="7">椰子</option>
     <option value="8">猕猴桃</option>
     <option value="9">桃子</option>
    </select>
    </div>
    </div>

$(window).on('load', function () {
 $('#usertype').selectpicker({
 'selectedText': 'cat'
 });
});

var str='3,4,5,6';
var arr=str.split(',');
$('#usertype').selectpicker('val', arr);