Abstract: For the electricity demand of small ocean observation instruments,an efficient and reliable energy conversion system of small hydraulic wave energy device is studied. A set of 3 kW hydraulic wave energy conversion system is established in the laboratory.Hydraulic system tests with different resistance,different energy storage volumes and different control strategies are carried out to obtain the PTO efficiency curve and the characteristic curve of each power generation process,to analyze the energy conversion characteristics of the different control strategies in detail. It is concluded that the PTO efficiency tends to be stable with the increase of resistance and the energy storage volume has no effects on the conversion efficiency of PTO. The feasibility of the direct impact energy conversion system with accumulator and without controller is verified.