string tempPath = this.Request.PhysicalApplicationPath + "web.config";
XmlDocument xd = new XmlDocument();
xd.Load(tempPath);
XmlNode xn = xd.SelectSingleNode("//add[@key='test']");//获取节点属性
XmlNode xn = xd.SelectSingleNode("/configration/appSetting/add[@key='test']");
Response.Write(xn.Attributes["value"].Value);