看了篇文章可能会用的上，直接贴过来了。

private bool UrlIsExist(String url)  {    System.Uri u = null;    try    {      u = new Uri(url);    }    catch { return false; }    bool isExist = false;    System.Net.HttpWebRequest r = System.Net.HttpWebRequest.Create(u) as System.Net.HttpWebRequest;    r.Method = "HEAD";    try    {      System.Net.HttpWebResponse s = r.GetResponse() as System.Net.HttpWebResponse;      if (s.StatusCode == System.Net.HttpStatusCode.OK)      {        isExist = true;      }    }    catch (System.Net.WebException x)    {      try      {        isExist = ((x.Response as System.Net.HttpWebResponse).StatusCode != System.Net.HttpStatusCode.NotFound);      }      catch { isExist = (x.Status == System.Net.WebExceptionStatus.Success); }    }    return isExist;  }  protected void Page_Load(object sender, EventArgs e)  {    Response.Write("
http://dotnet.aspx.cc/Images/ 是否存在：" + UrlIsExist("http://dotnet.aspx.cc/Images/"));    Response.Write("
http://dotnet.aspx.cc/ImagesX/ 是否存在：" + UrlIsExist("http://dotnet.aspx.cc/ImagesX/"));    Response.Write("
http://xxxxx/ 是否存在：" + UrlIsExist("http://xxxxx/"));    Response.Write("
hxxxxxxxxxxxxxxxxxxx 是否存在：" + UrlIsExist("hxxxxxxxxxxxxxxxxxxx"));    Response.Write("
http://dotnet.aspx.cc/Images/logoSite.gif 是否存在：" + UrlIsExist("http://dotnet.aspx.cc/Images/logoSite.gif"));    Response.Write("
http://dotnet.aspx.cc/Images/logoSite2.gif 是否存在：" + UrlIsExist("http://dotnet.aspx.cc/Images/logoSite2.gif"));  }

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