i've wondering here,if i can combine windows application and web aplication.Can i develop main page in web application then i want to access to the windows application.(e.g there's a button to link process mgt page.But process mgt page is developed in windows application).Else, if i do a view page on windows application and to retrieve the data is from web application. Example, users may fill the form through website, then to display the information is in windows application.Can i retrieve the data from the same database(SQL server dbase).

Yes you can but not in the picture you draw in your imagination, through WCF, web services, or even shared database on internet and each of which has its pros\cons.
- Clients should have windows application on machine they work on.
- Windows application won't be on web browser.
- There's no direct interaction.