using System.Xml;

public partial class _Default : System.Web.UI.Page

{

    protected void Page_Load(object sender, EventArgs e)

    {

        XmlDocument doc = new XmlDocument();

        doc.Load(Server.MapPath("data.xml"));

        XmlNode node = doc.DocumentElement;

        XmlNode book = node.SelectSingleNode ( "//book[@id='01']" );

        XmlElement bookName = doc.CreateElement ( "name" );

        bookName.InnerText = "Xiyouji";

        XmlAttribute numbers = doc.CreateAttribute ("numbers");

        numbers.Value = "100";

        bookName.Attributes.Append ( numbers );

        book.AppendChild ( bookName );

        doc.Save ( Server.MapPath ( "data.xml" ) );

    }

}

生成的XML文件内容为

<?xml version="1.0" encoding="gb2312"?>

<root>

  <library>

    <book id="01">

      <name numbers="100">Xiyouji</name>

    </book>

    <book id="02">

      <name numbers="100">Hongloumeng</name>

    </book>

  </library>

</root>