namespace 数据录入窗体
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnAdd_Click(object sender, EventArgs e)
        {
            string numbers = txtNumbers.Text;
            string name = txtName.Text;
            string address = txtAddress.Text;
            string classes = txtClass.Text;
            string phone = txtPhone.Text;

            using (SqlConnection conn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDBFilename=|DataDirectory|\db_Students.mdf;Integrated Security=True;User Instance=True"))
            {
                conn.Open();
                using(SqlCommand cmd = conn.CreateCommand())
                {
                     = "Insert into tb_students(numbers,name,address,classes,phone) values(@numbers,@name,@address,@classes,@phone)";
                    
                    //cmd.Parameters.Clear();
                    cmd.Parameters.Add(new SqlParameter("numbers", numbers));
                    cmd.Parameters.Add(new SqlParameter("name", name));
                    cmd.Parameters.Add(new SqlParameter("address", address));
                    cmd.Parameters.Add(new SqlParameter("classes", classes));
                    cmd.Parameters.Add(new SqlParameter("phone", phone));
                    cmd.ExecuteNonQuery();
                }
                MessageBox.Show("信息导入成功");
            }
        }

        private void btnExit_Click(object sender, EventArgs e)
        {
            this.Close();
        }
    }
}

你该不会没有刷新数据表看看吧...

刷一下看看

刷新也不行，我纳闷啊

cmd.Parameters.Add(new SqlParameter("@numbers", numbers));

对啊，那个参数写错啦，都应该要在前面加@这个符号

这样试试...
cmd.Parameters.AddWithValue("numbers", numbers);
cmd.Parameters.AddWithValue("name", name);
cmd.Parameters.AddWithValue("address", address);
cmd.Parameters.AddWithValue("classes", classes);
cmd.Parameters.AddWithValue("phone", phone);
cmd.ExecuteNonQuery();

加参数时前面要加@

感谢各位大侠的帮助，虽然不能每个都给分。还是谢谢大家了