The ocean contains mass of clean and renewable energy in many types, the wave energy is one of them. Though the wave energy is wildly distributed, its low quality needs the devices with special design to capture the energy efficiency. Shanghai Ocean University has proposed an impeller wheel wave energy generator. To ensure its efficiency, the impeller CFD analysis is required. In this article, the relationship of single grade impeller and distance of double grades was simulated and discussed. And finally find out the most appropriate design parameters.