please help me for this problem, why can't it trim this surface to hull ?
Trimming needs to form closed regions. So to trim to that deck plane, you need to lose the trim region across the transom.
You can do that be adding a transom surface, or you can just align the aft edge of your deck surface with the aft end of the hull surface.
You do need to specify which surfaces are being used to trim a surface. This is done through surface properties: