很容易尝试这样做：

右键单击解决方案资源管理器（您的ProjectName）和

然后点击!! 添加现有项目.. !!

然后选择旧的。您希望在新的网络应用程序中添加的aspx页面。

然后刷新您的文件夹它将显示您添加的.aspx页面。好吧！

感谢你！

It's Easy try to done it like this way:
Right click on your Solution explorer(Your ProjectName)and
Then Click on !!Add Existing item..!!
Then select your old .aspx pages which you want to add in your new webapplication.
Then Refresh your folder it will display your added .aspx pages.Okay!
Thanking You !