调试易

private void FrmMain_Load(object sender, EventArgs e)
        {
            ChangeSize(2);
        }
        private void ChangeSize(int type)
        {
            if(type==1)
            {
                this.Size = new Size(970, 515);               
            }
            else
            {
                this.Size = new Size(698, 515);               
            }
        }
   
  这样为什么不起作用？

好使
会根据
if(type==1) 
            { 
                this.Size = new Size(970, 515);                
            } 
            else 
            { 
                this.Size = new Size(698, 515);                
            } 
而改变你的是vs200?
你说的不起作用是什么

private void ChangeSize(int type)
        {
            if(type==1)
            {
                this.Size = new Size(970, 525);
                this.lable1.Visible = true;
            }
            else
            {
                this.Size = new Size(698, 525);
                this.lable1.Visible = false;
            }
        }        /// <summary>
        /// 监视Windows消息
        /// </summary>
        /// <param name="m"></param>
        protected override void WndProc(ref Message m)
        {
            const int WM_DEVICECHANGE = 0x219;
            const int WM_DEVICEARRVIAL = 0x8000;//如果m.Msg的值为0x8000那么表示有U盘插入
            const int WM_DEVICEMOVECOMPLETE = 0x8004;//U盘拔出
            switch (m.Msg)
            {
                case WM_DEVICECHANGE:
                    {
                        this.leftPanelTree.ShowDeviceChanged("WM_DEVICECHANGE");
                        if (m.WParam.ToInt32() == WM_DEVICEARRVIAL)
                        {
                            this.leftPanelTree.ShowDeviceChanged("WM_DEVICEARRVIAL");//U盘插入
                            ChangeSize(1);//能正常变大，lable1也会不可见
                        }
                        else if (m.WParam.ToInt32() == WM_DEVICEMOVECOMPLETE)
                        {
                            this.leftPanelTree.ShowDeviceChanged("WM_DEVICEMOVECOMPLETE");//U盘拔出
                            ChangeSize(2);//大小为什么会不变化？，但lable1会不可见
                        }
                    }
                    break;
            }
            base.WndProc(ref m); //将系统消息传递自父类的WndProc
        }

                        if (m.WParam.ToInt32() == WM_DEVICEMOVECOMPLETE)
                        {
                            this.leftPanelTree.ShowDeviceChanged("WM_DEVICEMOVECOMPLETE");//U盘拔出
                            ChangeSize(2);//大小为什么会不变化？，但lable1会不可见
                        }
                        
                        就是U盘拔出时不能正常变化大小？

你确定别的地方没设置lable1？
测试了你的代码 没啥问题

谢谢两位的关注，找到原因了，散分了private void ChangeSize(int type)
        {
            if(type==1)
            {
                this.Size = new Size(970, 525);
                this.lable1.Visible = true;
            }
            else
            {
                this.lable1.Visible = false;//移到前面就可以了，先false掉
                this.Size = new Size(698, 525);
                //this.lable1.Visible = false;
            }
        }