经大神启发后，才知道设置几个变量尤其是bool类型的方向，之后就是简单的判断了。

 // 当用户导航到此页面时执行。
        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
          
        }

        bool m_fx_x = true;                //方向
        bool m_fx_y = true;
        int m_speed_x = 10;                 //速度
        int m_speed_y = 5;
        public void move(object sender,EventArgs e)
        {
            

        
            if (m_fx_y == true)
            {
                double sp_s = Canvas.GetTop(ep_1) + m_speed_y;
                Canvas.SetTop(ep_1,sp_s);
            }
            else
            {
                double sp_s = Canvas.GetTop(ep_1) - m_speed_y;
                Canvas.SetTop(ep_1, sp_s);
            }


            if (m_fx_x == true)
            {
                double sp_s = Canvas.GetLeft(ep_1) + m_speed_x;
                Canvas.SetLeft(ep_1,sp_s);
            }
            else
            {
                double sp_s = Canvas.GetLeft(ep_1) - m_speed_x;
                Canvas.SetLeft(ep_1,sp_s);
            }

            if (Canvas.GetTop(ep_1) <=0 || Canvas.GetTop(ep_1) >= 340)    //Y轴运动
            {
                m_fx_y = !m_fx_y;
             //   Random rand = new Random();              随机y方向速度
             //   m_speed_y = 3 + rand.Next(0, 5);
            }
            if (Canvas.GetLeft(ep_1) <= 0 || Canvas.GetLeft(ep_1) >= 340)    //X轴运动
            {
                m_fx_x = !m_fx_x;
             //   Random rand = new Random();               随机x方向速度
              //  m_speed_x = 3 + rand.Next(0, 5);          
            }

        }

        private void Page_Loaded(object sender, RoutedEventArgs e)
        {

            DispatcherTimer timer = new DispatcherTimer();
            timer.Interval = TimeSpan.FromMilliseconds(70);
            timer.Tick += new EventHandler(move);
            timer.Start();
        }
    }