SqlConnection con = new SqlConnection(@"Data Source=.\SQLEXPRESS;User Instance=True;AttachDBFilename=D:\My Documents\Visual Studio 2008\Projects\FirstFace\FirstFace\bin\Debug\MyDB.mdf;Integrated Security=True");
             con.Open();
         //   Form4 form41 = new Form4();
            string string1 = "select * from student";
            SqlCommand cmd = new SqlCommand(string1, con);
            SqlDataReader rd = cmd.ExecuteReader();
            while (rd.Read())
            {
               form41.textBox1.Text = rd["id"].ToString().Trim();
               form41.textBox2.Text = rd["name"].ToString().Trim();
               form41.textBox4.Text = rd["age"].ToString().Trim();

            //   textBox10.Text = rd["age"].ToString().Trim();
            }
            rd.Close();
            con.Close();
          //  form41.Show();


 说 form41.textBox1.Text 不可访问？什么意思啊？那位大哥教教我！刚学C#

form41.textBox1 的modifier属性设置为public 就可以啦

解决了，谢了！

2楼的方法可以

哈哈