先上xml

<?xml version="1.0" encoding="utf-8" ?>
<SendExResp xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"  xmlns="urn:schemas-microsoft-com:office:spreadsheet">
  <PayCount>1</PayCount>
  <BlackWords />
  <ErrorMobiles />
  <BlackMobiles />
  <BatchSendID>00000000-0000-0000-0000-000000000000</BatchSendID>
  <Result>aaa</Result>
  <ErrorDesc>成功</ErrorDesc>
</SendExResp>

需要注意，xmlns后面跟:**与不跟，读取时是不同的，看后台代码

String path = System.AppDomain.CurrentDomain.BaseDirectory + "//return.xml";

            XmlDocument xmldoc = new XmlDocument();
            xmldoc.Load(path);

            XmlNamespaceManager namespaceManager = new XmlNamespaceManager(xmldoc.NaMetable); //namespace 
            namespaceManager.AddNamespace("xsi","http://www.w3.org/2001/XMLSchema-instance");
            namespaceManager.AddNamespace("xsd","http://www.w3.org/2001/XMLSchema");
            namespaceManager.AddNamespace("d","urn:schemas-microsoft-com:office:spreadsheet");
            XmlNode node = xmldoc.SelectSingleNode("descendant::d:Result",namespaceManager);

            if (node != null)
            {
                string s = node.InnerText;
            }

如果命 名空间都是xmlns:***这种的，写xmlpath的时候，就不需要带默认命名空间，例如上面的d:,可以直接用//SendExResp/Result就能取到这个节点的值，但是因为有一个命 名空间xmlns="urn:schemas-microsoft-com:office:spreadsheet"，xmlns后面没有跟:***,这时，就要把这个默认的命名空间给加在xml路径上。

descendant::表示取这个命名空间下的所有某个名称的节点,该写法参考了微软的官方说明，地址：http://msdn.microsoft.com/en-us/library/system.xml.xmlnode.selectsinglenode.aspx

怕有时候微软网站打不开，把它的代码粘在下面：

The example uses the file,newbooks.xml,as input.

<?xml version='1.0'?>
<bookstore xmlns="urn:newbooks-schema">
  <book genre="novel" style="hardcover">
    <title>The Handmaid's Tale</title>
    <author>
      <first-name>Margaret</first-name>
      <last-name>Atwood</last-name>
    </author>
    <price>19.95</price>
  </book>
  <book genre="novel" style="other">
    <title>The Poisonwood Bible</title>
    <author>
      <first-name>Barbara</first-name>
      <last-name>Kingsolver</last-name>
    </author>
    <price>11.99</price>
  </book>
</bookstore>

C#代码：

using System;
using System.IO;
using System.Xml;

public class Sample
{
  public static void Main()
  {

      XmlDocument doc = new XmlDocument();
      doc.Load("newbooks.xml");

      // Create an XmlNamespaceManager to resolve the default namespace.
      XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NaMetable);
      nsmgr.AddNamespace("bk","urn:newbooks-schema");

      // Select the first book written by an author whose last name is Atwood.
      XmlNode book;
      XmlElement root = doc.DocumentElement;
     book = root.SelectSingleNode("descendant::bk:book[bk:author/bk:last-name='Atwood']",nsmgr);

      Console.WriteLine(book.OuterXml);

  }
}