I want to migrate my database from SP 2007 to 2013 directly. My 2007 database has only one form, so we planned to create a same form in 2013 and copy the database. Is it possible?
No, you cannot. You must upgrade first to 2010.
You cannot upgrade directly from the server products in the Office 2007 release to SharePoint 2013. The changes between versions are too great, and the hardware requirements differ so much between versions that a direct upgrade is not possible or supported. However, you can perform a series of database-attach upgrades to first upgrade your content to SharePoint 2010 Products and then to SharePoint 2013. This article describes how to perform these sequential database-attach upgrades.
An alternative is 3rd party vendor migration tool: http://blogs.msdn.com/b/ronalg/archive/2013/01/28/can-i-upgrade-from-sharepoint-2007-directly-to-sharepoint-2013.aspx