XmlDocument xmlDoc = new XmlDocument();
xmlDoc.Load(Server.MapPath("XMLFile.xml"));
XmlNode root = xmlDoc.SelectSingleNode("Books");
XmlElement book = xmlDoc.CreateElement("Book");
XmlElement title = xmlDoc.CreateElement("Title");
title.InnerText = "XML";
book.AppendChild(title);
XmlAttribute attr = xmlDoc.CreateAttribute("attr");
attr.Value = "111";
title.Attributes.Append(attr);
XmlElement isbn = xmlDoc.CreateElement("ISBN");
isbn.InnerText = "333333";
book.AppendChild(isbn);
XmlElement author = xmlDoc.CreateElement("Author");
author.InnerText = "snow";
book.AppendChild(author);
XmlElement price = xmlDoc.CreateElement("Price");
price.InnerText = "120";
price.SetAttribute("Unit", "FCKpd___0quot");
book.AppendChild(price);
root.AppendChild(book);
xmlDoc.Save(Server.MapPath("XMLFile.xml"));