/// <summary>
        /// 获取指定节点的值
        /// </summary>
        /// <param name="strFileName">文件路径</param>
        /// <param name="nodeName">节点名称</param>
        /// <param name="value">设置后的值</param>
        /// <param name="nodeDir">指定节点所在的节点目录</param>
        /// <returns></returns>
        public static string GetNodeValue(string strFileName, string nodeName, string nodeDir)
        {
            string value = null;
            try
            {
                XmlDocument xmlDoc = new XmlDocument();
                xmlDoc.Load(strFileName);

                XmlNodeList nodeList = xmlDoc.SelectSingleNode(nodeDir).ChildNodes;//获取bookstore节点的所有子节点 

                foreach (XmlNode xn in nodeList)    //遍历所有子节点 
                {
                    XmlElement xe = (XmlElement)xn;  //将子节点类型转换为XmlElement类型 

                    if (xe.Name == nodeName)
                    {
                        value = xe.InnerText.Trim();

                        break;
                    }
                }
            }
            catch (Exception exp)
            {
                throw exp;
            }

            return value;
        ｝

[color=#FF0000]
GetNodeValue(filePath, "Main", "Result/Flag");[/color]

------解决方案--------------------
string str=@<?xml version=\"1.0\" encoding=\"gb2312\"?> 
<Result>
  <Main>
  <Flag>True</Flag>  
  <Code>000</Code>  
  <Message>操作成功</Message>  
  </Main>
</Result>
";
XmlDocument xml = new XmlDocument();
xml.LoadXml(str);
XmlNodeList xnl = xml.SelectNodes("../Result/Main");
  foreach (XmlNode item in xnl)
  {
 string Flag = item.SelectSingleNode("Flag").InnerText;
 string Code= item.SelectSingleNode("Code").InnerText;
 string Message  = item.SelectSingleNode("Message").InnerText;
 }

数据量很多就要用集合保存Flag Code和Message