http://msdn.microsoft.com/zh-cn/library/system.xml.linq.xstreamingelement(v=vs.100).aspx
直接用File.AppendText的方式写入就可以了~~~
SAX方法操作文件
http://stackoverflow.com/questions/3337953/working-with-very-huge-xml-file-in-c-sharp
http://www.codeproject.com/Articles/156982/How-to-Open-Large-XML-files-without-Loading-the-XM
搜索 c# work with big xml