RequiredFieldValidator 没有效果！！

protected void Add_Click(object sender, EventArgs e)
    {        string Xuehao = this.XueHao.Text.Trim();//学号
        string Name = this.Name.Text.Trim();//姓名 
        string XiBie = this.DropDownList1.SelectedItem.Text.ToString();//系别
        string BanJi = this.DropDownList2.SelectedItem.Text.ToString();//
        string Sex = this.UserSex.Text.Trim();
        string Phone = this.Phone.Text.Trim();//联系方式
        string Qq = this.Qq.Text.Trim();//QQ
        string Sushe = this.Sushe.Text.Trim();//宿舍号
        string Adds = this.Adds.Text.Trim();//家庭地址
        string J_Name= this.J_Name.Text.Trim();//家长姓名
        string J_workadds = this.J_worksadds.Text.Trim();//家长工作单位
        string others = this.others.Text.Trim();//备注
        string sql = "insert into Students_User(XueHao,Name,XiBie,BanJi,Sex,Phone,Qq,Sushe,Adds,J_Name,j_work,others) values('" + Xuehao + "','" + Name + "','" + XiBie + "','" + BanJi + "','" + Sex + "','"+Phone+"','"+Qq+"','"+Sushe+"','"+Adds+"','"+J_Name+"','"+J_workadds+"','"+others+"')";
        DB.execnonsql(sql);
        this.XueHao.Text = "";
        this.Name.Text = "";
        this.Phone.Text = "";
        this.Qq.Text="";
        this.Qq.Text="";
        this.Sushe.Text="";
        this.Adds.Text="";
        this.J_Name.Text="";
        this.J_worksadds.Text="";
        this.others.Text ="";
        
        // this.Label1.Text = "您已经发成功！！";
        // this.Label1.Visible = true;
        Page.ClientScript.RegisterStartupScript(this.GetType(), "Startup", "<script>alert('成功增加一名学生！！！！')</script>");//无刷新弹出对话框
        return;
    }为什么会提交数据！！！！！！！！！！