Please refer the follwing.
Ref
http://msdn.microsoft.com/en-us/library/c22k3d47.aspx
Initial XML
<?xml version="1.0" encoding="utf-8"?>
<Details>
</Details>
C#
protected void Page_Load(object sender, EventArgs e)
{
string filename = Server.MapPath("~/XMLFile.xml");
XmlDocument doc = new XmlDocument();
doc.Load(filename);
XmlNode node = doc.CreateNode(XmlNodeType.Element, "Data", null);
XmlNode nodeName = doc.CreateElement("Student", "FirstName", "Student:FirstName");
nodeName.InnerText = "Name";
XmlNode nodeAge = doc.CreateElement("Student", "Age", "Student:Age");
nodeAge.InnerText = "25";
node.AppendChild(nodeName);
node.AppendChild(nodeAge);
doc.DocumentElement.AppendChild(node);
doc.Save(filename);
}
XML data when page is running
<?xml version="1.0" encoding="utf-8"?>
<Details>
<Data>
<Student:FirstName xmlns:Student="Student:FirstName">Name</Student:FirstName>
<Student:Age xmlns:Student="Student:Age">25</Student:Age>
</Data>
</Details>
If you do not want to have the colon the refer this code
protected void Page_Load(object sender, EventArgs e)
{
string filename = Server.MapPath("~/XMLFile.xml");
XmlDocument doc = new XmlDocument();
doc.Load(filename);
XmlNode node = doc.CreateNode(XmlNodeType.Element, "Data", null);
XmlNode nodeName = doc.CreateElement( "FirstName",null);
nodeName.InnerText = "Name";
XmlNode nodeAge = doc.CreateElement( "Age", null);
nodeAge.InnerText = "25";
node.AppendChild(nodeName);
node.AppendChild(nodeAge);
doc.DocumentElement.AppendChild(node);
doc.Save(filename);
}
Xml format
<?xml version="1.0" encoding="utf-8"?>
<Details>
<Data>
<FirstName>Name</FirstName>
<Age>25</Age>
</Data>
</Details>