Not really, no.
The best way to a flat stomach is reducing fat in the abdominal area. The problem is the fat in your body does not depend on where you want it to sit. So what you have to do is reduce the fat all over (if you have a high fat percentage of course).
Contrary to popular conception, situps do not really get you a flat stomach, and they do not even promist a six pack look. Working on your stomach area is important for other reasons, so don't neglect it. Don't forget to work on your back area as well.