This paper discusses the energy matching problem between wave energy input and generator power output, in the power performance assessment for the energy storage type of wave energy converter. Under the small wave condition, the power performance of the energy storage type of wave energy converter is researched. The site test data processing method is analyzed, and the calculation method of the average conversion efficiency and the annual energy production are optimized. The results show that the optimized power performance analysis method can more accurately assess the power performance matrix of the wave energy converter, and improve the calculation accuracy of the average conversion efficiency and the annual energy production of the wave energy converter. The research results provide an effective method for more scientific and accurate evaluation of power performance indexes of the energy storage type of wave energy converters.