public class UpperCaseUTF8Encoding : UTF8Encoding
{
  // Code from a blog http://www.distribucon.com/blog/CategoryView,category,XML.aspx
  //
  // Dan Miser - Thoughts from Dan Miser
  // Tuesday, January 29, 2008 
  // He used the Reflector to understand the heirarchy of the encoding class
  //
  //      Back to Reflector, and I notice that the Encoding.WebName is the property used to
  //      write out the encoding string. I now create a descendant class of UTF8Encoding.
  //      The class is listed below. Now I just call XmlTextWriter, passing in
  //      UpperCaseUTF8Encoding.UpperCaseUTF8 for the Encoding type, and everything works
  //      perfectly. - Dan Miser

  public override string WebName
  {
    get { return base.WebName.ToUpper(); }
  }

  public static UpperCaseUTF8Encoding UpperCaseUTF8
  {
    get
    {
      if (upperCaseUtf8Encoding == null) {
        upperCaseUtf8Encoding = new UpperCaseUTF8Encoding();
      }
      return upperCaseUtf8Encoding;
    }
  }  

  private static UpperCaseUTF8Encoding upperCaseUtf8Encoding = null;
}

利用这一习俗,你需要使用XMLTextWriter作为XDocument Save方法的目的地。

// This section not shown in the blog

var xDoc = XDocument.Load(xmlDocNm); //This is your xml path value 
// Changes to XML Document here

// .Net writes the XML declaration using lower case utf-8.
//  <?xml version="1.0" encoding="utf-8"?>
// It is not suppesed to matter but NiceForm expects the delcaration to be uppercase.
//  <?xml version="1.0" encoding="UTF-8"?>
// We are using a XMLWriter with a custom Encoding to captialize the UTF

// Set various options to retrive the desired output
var settings = new XmlWriterSettings {
  Encoding = new UpperCaseUTF8Encoding(), // Key setting option for this example

  NewLineHandling = System.Xml.NewLineHandling.Replace,
  NewLineOnAttributes = true,
  Indent = true                           // Generate new lines for each element
};

using (var xmlWriter =XmlTextWriter.Create(xmlDocNm, settings)) {
  xDoc.Save(xmlWriter);
}