这就是我在custom。css中所做的，我添加了这些行，仅此而已。

.modal-lg {
    width: 600px!important;
    margin: 0 auto;
}

显然，你可以改变宽度的大小。

我用过这种方法，非常适合我

$("#my-modal")
.modal("toggle")
.css({'width': '80%', 'margin-left':'auto', 'margin-right':'auto', 'left':'10%'});

在Bootstrap 3 CSS中，你可以简单地使用:

body .modal-dialog {
    /* percentage of page width */
    width: 40%;
}

这确保了你不会破坏页面的设计，因为我们使用的是。modal-dialog而不是。modal，后者甚至会被应用到底纹上。

保留响应式设计，将宽度设置为您想要的。

.modal-content {
  margin-left: auto;
  margin-right: auto;
  max-width: 360px;
}

保持简单。

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>

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;
        }