1、DataTable转换成XML
public string ConvertDataTableToXML(DataTable xmlDS)
        {
            MemoryStream stream = null;
            XmlTextWriter writer = null;
            try
            {
                stream = new MemoryStream();
                writer = new XmlTextWriter(stream, Encoding.UTF8);
                xmlDS.WriteXml(writer);
                int count = (int)stream.Length;
                byte[] arr = new byte[count];
                stream.Seek(0, SeekOrigin.Begin);
                stream.Read(arr, 0, count);
                UTF8Encoding utf = new UTF8Encoding();
               
                return utf.GetString(arr).Trim();
            }
            catch
            {
                return String.Empty;
            }
            finally
            {
                if (writer != null) writer.Close();
            }
        }

 2、XML转换成DataTable
        private DataSet ConvertXMLToDataSet(string xmlData)
        {
            StringReader stream = null;
            XmlTextReader reader = null;
            try
            {
                DataSet xmlDS = new DataSet();
                stream = new StringReader(xmlData);
                reader = new XmlTextReader(stream);
                xmlDS.ReadXml(reader);
                return xmlDS;
            }
            catch (Exception ex)
            {
                string strTest = ex.Message;
                return null;
            }
            finally
            {
                if (reader != null)
                    reader.Close();
            }
        }