A multifunctional large offshore buoy capable of diving and based on a green energy source comprises an upper layer structure and a ballast water spherical cabin. The multifunctional large offshore buoy is characterized in that the upper layer structure and the ballast water spherical cabin are connected through a framework, anchor beds are connected to an anchor chain retracting and releasing wheel below the ballast water spherical cabin through anchor chains, a water turbine is mounted on the ballast water spherical cabin, and the ballast water spherical cabin is internally provided with a seawater desalting device and a water storage tank; and the water turbine is provided with a power supply line group which is connected with the seawater desalting device, the seawater desalting deviceis provided with water inlet pipes which are arranged in seawater, a water outlet pipe is connected with the water storage tank, and the water storage tank is connected with a water outlet pipeline.The multifunctional large offshore buoy capable of diving and based on the green energy source has the beneficial effects that 1, wind, solar and tidal flow combined power generating is utilized to continuously supply power to the buoy, and the green and the environmental protection effects are achieved; 2, a high-definition camera is mounted, the defect that traditional radar cannot accurately track a small ship is overcome, and safety of water area near a port is ensured; and 3, excess electricity can be used for conducting seawater desalting, and the storage amount of ballast water is automatically adjusted according to the seawater amount obtained after desalting.