JS
 function people_modif() {
        var vURL = "admin_action.ashx?&rand=" + Math.random();
        $("#peopledetail").ajaxSubmit({
            url:encodeURI(vURL), 
            type: "post",
            dataType: "text",
            success: function (str) {
                
            },
            error: function (error) {
            }
        });
    }

HTML:
<div style=" float:left">更新图片：<input id="popmodifimage" type="file"  name="popmodifimage" /></div>

后台代码 action.ashx

HttpPostedFile pf = Request.Files["popmodifimage"];
if (pf != null)
{
    string fileExtension = System.IO.Path.GetExtension(pf.FileName); //上传文件的扩展名
    if (fileExtension != ".jpg" && fileExtension != ".gif" && fileExtension != ".bmp" && fileExtension != "png")
    {
        Response.Write("-1");
        return;
    }
    fileName = DateTime.Now.ToString("yyyyMMddHHmmss") + fileExtension; //给文件重新命名
    pf.SaveAs(path + fileName);

    if (mpopimgurl != "") File.Delete(path + mpopimgurl);
    strimg = " ,ImageUrl=@imageurl ";
}