/// <summary>
/// 用户实体类
///
/// 注意：类的访问修饰符必须是：public，否则会出现错误：
/// 因其保护级别而不可访问。只能处理公共类型。
/// </summary>
[Serializable]
public class UserModel
{
    private long id = 1;
    private string name = "name";
    private int gender = 0;
    private int age = 20;
    private string userName = "userName";
    private string password = "password";
    public long Id
    {
      get { return id; }
      set { id = value; }
    }
    public string Name
    {
      get { return name; }
      set { name = value; }
    }
    public int Gender
    {
      get { return gender; }
      set { gender = value; }
    }
    public int Age
    {
      get { return age; }
      set { age = value; }
    }
    public string UserName
    {
      get { return userName; }
      set { userName = value; }
    }
    public string Password
    {
      get { return password; }
      set { password = value; }
    }
}

private void button1_Click(object sender, EventArgs e)
{
  try
  {
    List<UserModel> list = new List<UserModel>();
    list.Add(new UserModel());
    list.Add(new UserModel());
    list.Add(new UserModel());
    list.Add(new UserModel());
    list.Add(new UserModel());
    list.Add(new UserModel());
    list.Add(new UserModel());
    list.Add(new UserModel());
    list.Add(new UserModel());
    list.Add(new UserModel());
    using (System.IO.StringWriter stringWriter = new StringWriter(new StringBuilder()))
    {
      XmlSerializer xmlSerializer = new XmlSerializer(typeof(List<UserModel>));
      xmlSerializer.Serialize(stringWriter, list);
      FileStream fs = new FileStream("list_userModel.xml", FileMode.OpenOrCreate);
      StreamWriter sw = new StreamWriter(fs);
      sw.Write(stringWriter.ToString());
      sw.Close();
      fs.Close();
      MessageBox.Show("写入文件成功！");
    }
  }
  catch (System.Exception ex)
  {
    System.Console.WriteLine("====================================");
    System.Console.WriteLine(ex.Message);
    System.Console.WriteLine(ex.StackTrace);
  }
}

<?xml version="1.0" encoding="utf-16"?>
<ArrayOfUserModel xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
 <UserModel>
  <Id>1</Id>
  <Name>name</Name>
  <Gender>0</Gender>
  <Age>20</Age>
  <UserName>userName</UserName>
  <Password>password</Password>
 </UserModel>
 <UserModel>
  <Id>1</Id>
  <Name>name</Name>
  <Gender>0</Gender>
  <Age>20</Age>
  <UserName>userName</UserName>
  <Password>password</Password>
 </UserModel>
 <UserModel>
  <Id>1</Id>
  <Name>name</Name>
  <Gender>0</Gender>
  <Age>20</Age>
  <UserName>userName</UserName>
  <Password>password</Password>
 </UserModel>
 <UserModel>
  <Id>1</Id>
  <Name>name</Name>
  <Gender>0</Gender>
  <Age>20</Age>
  <UserName>userName</UserName>
  <Password>password</Password>
 </UserModel>
 <UserModel>
  <Id>1</Id>
  <Name>name</Name>
  <Gender>0</Gender>
  <Age>20</Age>
  <UserName>userName</UserName>
  <Password>password</Password>
 </UserModel>
 <UserModel>
  <Id>1</Id>
  <Name>name</Name>
  <Gender>0</Gender>
  <Age>20</Age>
  <UserName>userName</UserName>
  <Password>password</Password>
 </UserModel>
 <UserModel>
  <Id>1</Id>
  <Name>name</Name>
  <Gender>0</Gender>
  <Age>20</Age>
  <UserName>userName</UserName>
  <Password>password</Password>
 </UserModel>
 <UserModel>
  <Id>1</Id>
  <Name>name</Name>
  <Gender>0</Gender>
  <Age>20</Age>
  <UserName>userName</UserName>
  <Password>password</Password>
 </UserModel>
 <UserModel>
  <Id>1</Id>
  <Name>name</Name>
  <Gender>0</Gender>
  <Age>20</Age>
  <UserName>userName</UserName>
  <Password>password</Password>
 </UserModel>
 <UserModel>
  <Id>1</Id>
  <Name>name</Name>
  <Gender>0</Gender>
  <Age>20</Age>
  <UserName>userName</UserName>
  <Password>password</Password>
 </UserModel>
</ArrayOfUserModel>