A hydraulic wave energy generating device includes an absorbing device, a converting device and a generating device. The absorption device is composed of a float and a connecting rod, and the float is immersed in seawater. The conversion device and the power generation device are arranged in the buoy body. The conversion device is composed of a hydraulic cylinder, a supercharger, a reversing valve, a speed regulating valve, an accumulator, and a hydraulic motor. The float moves up and down under the action of waves, and the hydraulic cylinder piston moves up and down through the connecting rod. The hydraulic oil drives the hydraulic motor to rotate through the supercharger, reversing valve, and speed control valve. The accumulator plays the role of energy storage and voltage stabilization. The power generation device is composed of a generator, and the hydraulic motor is connected with the generator with a coupling to drive the generator to generate electricity. The invention mainly uses the hydraulic system to transfer energy, and realizes the conversion from ocean wave energy to buoy mechanical energy, then to hydraulic energy, then to motor mechanical energy, and finally to electric energy. The hydraulic wave energy generating device has a simple structure and is easy to install, and can be well applied to small ocean buoys.