i want create all part of my web site (Only GUI Layer in 3 tire technology) in App_Data Folder
You need to know what App_Data folder does, post which you would know what you ask. 3-tier application is totally different and App_Data is part of 1st/front end layer.
App_Data: Contains application data files including .mdf database files, XML files, and other data store files. The App_Data folder is used by ASP.NET to store an application's local database, such as the database for maintaining membership and role information
Read more here: MSDN: ASP.NET Web Project Folder Structure