使用Bootstrap 3，所需要的只是通过CSS给模态对话框一个百分比值

CSS

#alertModal .modal-dialog{
     width: 20%;
}

尝试以下内容(参见jsfiddle示例:http://jsfiddle.net/periklis/hEThw/1/)

<a class="btn" onclick = "$('#myModal').modal('show');$('#myModal').css('width', '100px').css('margin-left','auto').css('margin-right','auto');" ref="#myModal" >Launch Modal</a>
<div class="modal" id="myModal" style = "display:none">
  <div class="modal-header">
    <a class="close" data-dismiss="modal">×</a>
    <h3>Modal header</h3>
  </div>
  <div class="modal-body">
    <p>One fine body…</p>
  </div>
  <div class="modal-footer">
    <a href="#" class="btn">Close</a>
    <a href="#" class="btn btn-primary">Save changes</a>
  </div>
</div>​

在Bootstrap 3中，你所需要的就是这个

<style>
    .modal .modal-dialog { width: 80%; }
</style>

上面的大部分答案对我来说都没用!!

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.5/js/bootstrap.min.js"></script> <link href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.5/css/bootstrap.min.css" rel="stylesheet" /> <style> #myModal1 .modal-dialog { width: 80%; } #myModal2 .modal-dialog { width: 50%; } </style> <button type="button" class="btn btn-primary btn-lg" data-toggle="modal" data-target="#myModal1"> 80% </button> <button type="button" class="btn btn-primary btn-lg" data-toggle="modal" data-target="#myModal2"> 50% </button> <center> <!-- Modal --> <div class="modal fade" id="myModal1" tabindex="-1" role="dialog" aria-labelledby="myModalLabel"> <div class="modal-dialog" role="document"> <div class="modal-content"> <div class="modal-header"> <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span> </button> <h4 class="modal-title" id="myModalLabel">Modal title</h4> </div> <div class="modal-body"> custom width : 80% </div> <div class="modal-footer"> <button type="button" class="btn btn-default" data-dismiss="modal">Close</button> <button type="button" class="btn btn-primary">Save changes</button> </div> </div> </div> </div> <!-- Modal --> <div class="modal fade" id="myModal2" tabindex="-1" role="dialog" aria-labelledby="myModalLabel"> <div class="modal-dialog" role="document"> <div class="modal-content"> <div class="modal-header"> <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span> </button> <h4 class="modal-title" id="myModalLabel">Modal title</h4> </div> <div class="modal-body"> custom width : 50% </div> <div class="modal-footer"> <button type="button" class="btn btn-default" data-dismiss="modal">Close</button> <button type="button" class="btn btn-primary">Save changes</button> </div> </div> </div> </div> </center>

达到预期效果使用，

.modal-dialog {
    width: 41% !important;
}

you can use any prefix or postfix name for modal. but you need to make sure that's should use everywhere with same prefix/postfix name.    

body .modal-nk {
        /* new custom width */
        width: 560px;
        /* must be half of the width, minus scrollbar on the left (30px) */
        margin-left: -280px;
    }

or

body .nk-modal {
            /* new custom width */
            width: 560px;
            /* must be half of the width, minus scrollbar on the left (30px) */
            margin-left: -280px;
        }

基于较少的解决方案(无js) Bootstrap 2:

.modal-width(@modalWidth) {
    width: @modalWidth;
    margin-left: -@modalWidth/2;

    @media (max-width: @modalWidth) {
        position: fixed;
        top:   20px;
        left:  20px;
        right: 20px;
        width: auto;
        margin: 0;
        &.fade  { top: -100px; }
        &.fade.in { top: 20px; }
    }
}

然后无论你想指定一个模态宽度:

#myModal {
    .modal-width(700px);
}