Try This Code
Using System.Data.SqlClient Objcet
try
{
string command = @"BACKUP DATABASE DBDemo TO DISK='"+ strFileName+"'";
SqlCommand oCommand = null;
SqlConnection oConnection = null;
oConnection = new SqlConnection("Data Source=MYPC/SQLEXPRESS;Initial Catalog=DBDemo;Integrated Security=True");
if (oConnection.State != ConnectionState.Open)
oConnection.Open();
oCommand = new SqlCommand(command, oConnection);
oCommand.ExecuteNonQuery();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}