可使用以下代码：

//Create our own namespaces for the output
XmlSerializerNamespaces ns = new XmlSerializerNamespaces ();

//Add an empty namespace and empty value
ns.Add ("", "");

//Create the serializer
XmlSerializer slz = new XmlSerializer (someType);

//Serialize the object with our own namespaces (notice the overload)
slz.Serialize (myXmlTextWriter, someObject, ns);

此外，在评论中还提到了去除开头的<?xml version="1.0" encoding="utf-8"?>的方法：

XmlWriterSettings settings = new XmlWriterSettings ();

// Remove the <?xml version="1.0" encoding="utf-8"?>
settings.OmitXmlDeclaration = true;

XmlWriter writer = XmlWriter.Create ("output_file_name.xml", settings);



另外，如果出现开头没有encoding="utf-8"时，应该使用：

XmlWriterSettings settings = new XmlWriterSettings ();

settings.Encoding = Encoding.UTF8;

XmlWriter writer = XmlWriter.Create ("output_file_name.xml", settings);