The development of new energy has become a historical trend and an inevitable choice in today's world, facing the problem that the possible greenhouse gas emissions and the decline of traditional fossil reserves including oil and coal. Marine energy is a renewable energy source that is green, clean and has huge reserves. The oscillating wave energy converter can effectively convert wave energy into power resources for human society. In this paper, an oscillating wave energyconverting device based on artificial breakwater is designed. Wave energy is captured by a buoy floating on the water, and then electricity generated with rotating generator driven by hydraulic power take-off (PTO) system. Design of the overall wave energy converter device is introduced in this paper. In addition, hydrodynamic parameters of the buoy are analysed by ANSYS/AQWA software including additional mass, damping coefficient and RAO. After that, the parameters of linear PTO are analysed with MATLAB/Simulink software. The hydraulic PTO system is designed and its electromechanical system is simulated with AMESim software. In addition, the damping is optimized with the simulation results of linear PTO and hydraulic PTO. The motion limitation of the buoy is accomplished by introducing the damping in PTO system. Finally, the feasibility of the designed hydraulic PTO system is examined by setting up a test bench.