public static void GetAllValue()
        {
            XmlDocument xmlDoc = new XmlDocument();
            xmlDoc.Load("..\\..\\test.xml");
            XmlNodeList xnList = xmlDoc.DocumentElement.SelectNodes("//item/item/item");
            foreach (XmlNode item in xnList)
            {
                Console.WriteLine(item.InnerText);
            }
        }

        public static void GetAllValueById(string id)
        {
            XmlDocument xmlDoc = new XmlDocument();
            xmlDoc.Load("..\\..\\test.xml");
            XmlNodeList xnList = xmlDoc.DocumentElement.SelectNodes("//item/item/item[@id='" + id + "']");
            foreach (XmlNode item in xnList)
            {
                Console.WriteLine(item.InnerText);
            }
        }

------解决方案--------------------
XmlDocument xml = new XmlDocument();
xml.Load("file");
xml.Attribute["id"] ="target" ;

2.
xml.SelectSingleNode("节点名").InnerText；


方法很多。