string updatacmd = "update g_user set name='" + txt_name.Text + "',card='" + txt_card.Text + "',riqi='" + txt_money.Text + "',gtel='" + txt_gtel.Text + "',tel='" + txt_tel.Text + "',email='" + txt_email.Text + "',youbian='" + txt_youbian.Text + "',address='" + txt_add.Text + "',sex='" + txt_sex.Text + "',danbaoren='" + txt_danbaoren.Text + "', job='" + txt_joy.Text + "' where id='" + txt_serch.Text + "'";

public bool getupdata()
    {
        bool flag = false;
        SqlConnection conn = null;
        dbcon db = new dbcon();

        string updatacmd = "update g_user set name='" + txt_name.Text + "',card='" + txt_card.Text + "',riqi='" + txt_money.Text + "',gtel='" + txt_gtel.Text + "',tel='" + txt_tel.Text + "',email='" + txt_email.Text + "',youbian='" + txt_youbian.Text + "',address='" + txt_add.Text + "',sex='" + txt_sex.Text + "',danbaoren='" + txt_danbaoren.Text + "', job='" + txt_joy.Text + "' where id='" + txt_serch.Text + "'";

        try
        {
            conn = db.getcon();
            conn.Open();
            SqlCommand cmd = new SqlCommand();
            cmd.CommandText = updatacmd;
            cmd.Connection = conn;
            cmd.ExecuteNonQuery();
            return true;

        }
        catch { return false;}
       finally{
           conn.Close();
        }
        return flag;

    }

    protected void btn_tj_Click(object sender, EventArgs e)
    {
        if (getupdata())
        {
            Response.Write("<script>alert('修改成功！')</script>");
            Response.Redirect("admin_.aspx");
           
        }
        else
            lab_message.Text = "修改失败！！！";
         
    }

------解决方案--------------------
是报错还是更新不成功，你把语句打印处理看看。
sql语法上没有错误啊。
只要不是int等类型，即使更新为''也不会有问题。
如果是更新不成功，会不会是主键txt_serch没有值。 where id='" + txt_serch.Text + "'