The invention discloses an offshore wind and wave complementary generating system and belongs to the technical field of energy development and utilization. The invention is used for overcoming a defect that a single offshore generating set is instable. The offshore wind and wave complementary generating system comprises a wind energy conversion device, a wave energy conversion device and a hydraulic conversion system, wherein the wind energy conversion device and the wave energy conversion device are respectively connected with the hydraulic conversion system; the wind energy conversion device is used for converting wind energy into mechanical energy and transmitting the mechanical energy to the hydraulic conversion system; the wave energy conversion device is used for converting wave energy into mechanical energy and transmitting the mechanical energy to the hydraulic conversion system; and the hydraulic conversion system serves as an energy conversion link and is used for convertingthe mechanical energy transmitted by the wind energy conversion device and the wave energy conversion device into hydraulic energy, superposing the hydraulic energy and driving a direct-drive generator to output electric energy. The stability of the output power of the offshore generating system is obviously improved.