<?xml version="1.0" standalone="yes"?>
<users>
  <xs:schema id="users" xmlns="" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
    <xs:element name="users" msdata:IsDataSet="true" msdata:Locale="en-US">
      <xs:complexType>
        <xs:choice minOccurs="0" maxOccurs="unbounded">
          <xs:element name="user"><!--这里是表名-->
            <xs:complexType>
              <xs:sequence>
                <xs:element name="userName" type="xs:string" minOccurs="0" msdata:Ordinal="0" />
                <xs:element name="userPass" type="xs:string" minOccurs="0" msdata:Ordinal="1" />
              </xs:sequence>
              <xs:attribute name="id" type="xs:int" />
            </xs:complexType>
          </xs:element>
        </xs:choice>
      </xs:complexType>
    </xs:element>
  </xs:schema>
</users>

        string s = File.ReadAllText(Server.MapPath("~/test.xml"));
        string xmlStr = s.Replace("xs:", "");
        XmlDocument xmlDoc = new XmlDocument();
        xmlDoc.LoadXml(xmlStr);
        XmlNodeList names = xmlDoc.SelectNodes(@"//element[@name='user']//*/@name");
        foreach (XmlNode name in names)
            Response.Write(name.Value + "<br/>");

------解决方案--------------------
C# code

            XmlDocument xDoc = new XmlDocument();
            xDoc.Load("..\\..\\test2.xml");
            XmlNamespaceManager xnm = new XmlNamespaceManager(xDoc.NameTable);
            xnm.AddNamespace("xs", "http://www.w3.org/2001/XMLSchema");
            XmlNodeList xNodes = xDoc.DocumentElement.SelectNodes("//*/xs:choice/xs:element/*//*[@name]", xnm);
            foreach (XmlNode item in xNodes)
            {
                Console.WriteLine(item.Attributes["name"].Value);
            }
            //输出：
            //userName
            //userPass
            //id