我不确定您的XML结构有什么特别之处.

I am not sure what is special about your XML structure.

我写的代码几乎没有什么

I would write the code little differently

string xmlNamespace = String.Empty;
XmlNamespaceManager nsmgr;
XmlNodeList nodeInfo = FABRequestXML.GetElementsByTagName("RootNodeName");
xmlNamespace = Convert.ToString(nodeInfo[0].Attributes["xmlns"].Value);
nsmgr = new XmlNamespaceManager(MyXml.NameTable);
nsmgr.AddNamespace("AB", xmlNamespace);

XmlNode myNode = MyXml.DocumentElement.SelectSingleNode("AB:NodeName", nsmgr);

希望有帮助