我建议用隐藏的iframe代替ajax请求，然后当服务器返回上述文件时，它将自动要求用户下载它。

//name of iframe
var strName = ("uploader" + (new Date()).getTime());
// the iframe
var jFrame = $( "<iframe name=\"" + strName + "\" src=\"about:blank\" />" ).css( "display", "none" );

jFrame.load(function( objEvent ){     
    // at this point the user should have been asked to download a file.

    // Remove the iFrame from the document.
    // Because FireFox has some issues with
    // "Infinite thinking", let's put a small
    // delay on the frame removal.
    setTimeout(function(){
        jFrame.remove();
    },100);
});

var form = $('<form>').attr( "action", "upload_act.cfm" )
    .attr( "method", "post" )
    .attr( "enctype", "multipart/form-data" )
    .attr( "encoding", "multipart/form-data" )
    .attr( "target", strName );

form.append('<input type="hidden" name="somename">').val("someval");

$( "body:first" ).append( jFrame, form );

（以上代码原始改编自http://www.bennadel.com/blog/1244-ColdFusion-jQuery-And-AJAX-File-
Upload-Demo.htm）

另一种选择是将其分为两个步骤。步骤1生成文件并返回url，步骤2用户单击下载（这将是指向该url的锚标记）。