我可以正常使用了... http://www.bootply .com/WAwE3QyUdb

I got it working ok...http://www.bootply.com/WAwE3QyUdb

在模态主体内的容器中添加一个col.

Add a col to the container inside the modal-body.

<div class="modal-dialog">
    <div class="modal-content">
        <div class="modal-header">
            <h3>Modal header</h3>
        </div>

        <div class="modal-body">
            <div class="container col-md-12">
                <div class="row">
                    <div class="col-md-3">
                        1st col 3
                    </div>

                     <div class="col-md-3">
                         2nd col 3
                     </div>

                     <div class="col-md-3">
                         3rd col 3</div>
                     </div>
                 </div>
             </div>
         </div>
    </div>
</div>