//创建XML文件对象的实例doc

XmlDocument doc = new XmlDocument();

//加载XML文件

doc.Load(HttpContext.Current.Server.MapPath("XMLFile.xml"));

foreach (XmlNode node in xmlDoc.SelectNodes("//CLASS_VALUE")) // 这个CLASS_VALUE是标签，它里面有id和name

{  //遍历每个CLASS_VALUE节点
   string strID = node.Attributes["id"].Value;
string strName = node.Attributes["name"].Value;
//要遍历子标签在这继续foreach循环
}

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XmlDocument xmlDoc = new XmlDocument();

xmlDoc.Load(HttpContext.Current.Server.MapPath("test.xml"));

XmlNode td = xmlDoc.SelectSingleNode("tr");

XmlElement newElement = xmlDoc.CreateElement("a");

XmlAttribute attr = xmlDoc.CreateAttribute("href");

attr.Value = "222.jpg";

newElement.Attributes.SetNamedItem(attr);

td.AppendChild(newElement);

xmlDoc.Save("D:\\test.xml");

Console.WriteLine(xmlDoc.InnerText);