The invention relates to an offshore wind power generation system with seabed compressed air energy storage. The system comprises an offshore wind power generation unit, an air compression and expansion power generation unit and a seabed high pressure air energy storing device. When electricity generated by the offshore power generation unit exceeds the demand of a power grid, an air compressor ofthe air compression and expansion power generation unit is driven by surplus electricity to fill the seabed high pressure air energy storing device with high pressure air; when the load of the powergrid is increased while the load of the offshore wind power generation unit cannot meet the demand of the power grid, high pressure air in the seabed high pressure air energy storing device is released, and an expansion machine of the air compression and expansion power generation unit acts to drive a power generator to generate power so as to provide a power load to the power grid. According to the invention, energy is stored by means of compressed air to absorb surplus power when the wind power is relatively great and the demand on the load of the power grid is low while the compressed air stored in the seabed expands to act when the wind power is relatively small or the demand on the load of the power grid is high to provide power to the power grid, so that a power regulating function of the wind power generation system is achieved.