try
            {
                OleDbConnection thisConnection = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=I:\C#\学生管理系统\student\student\db\student.mdb");
                thisConnection.Open();
                string sqlString = "SELECT   *   from   user";
                OleDbCommand cmd = new OleDbCommand(sqlString, thisConnection);
                OleDbDataReader thisReader = cmd.ExecuteReader();
                while (thisReader.Read())
                {
                    if ((name == thisReader["usename"]) && (pwd == thisReader["password"]))
                    {
                        this.Hide();
                        new main().Show();
                    }
                    else
                    {
                        MessageBox.Show("用户名或密码错误，请重新输入！");
                        textBox1.Clear();
                        textBox2.Clear();
                    }
                }
            }
            catch (Exception ee)
            {
                MessageBox.Show(ee.Message.ToString());
            }

里面哪里错了呀？

你试试把string sqlString = "SELECT   *   from   user";
改成string sqlString = "SELECT   *   from   [user]";

已解决
原来是USER是C#的关键字