The invention relates to a ship propeller, which comprises a pushing mechanism and a driving mechanism. The ship propeller is characterized in that the pushing mechanism comprises a cylinder sleeve, a piston, a piston connecting rod and a pressure-limiting automatic valve opening device, wherein the piston is sleeved in the cylinder sleeve, one end of the piston connecting rod is hinged with the piston, the other end of the piston connecting rod is connected with the driving mechanism, and the piston is provided with a valve rod hole and a ventilation hole; and the pressure-limiting automatic valve opening device comprises a valve, a valve rod, a spring and a spring bottom plate, wherein the valve is of a disk shape, the valve rod is inserted into the valve rod hole, one end of the valve rod is connected with the valve, the other end of the valve rod is connected with the spring bottom plate, and the spring is arranged between the piston and the spring bottom plate and is sleeved on the valve rod. The ship propeller has the beneficial effects that the ship propeller is simple in structure, low in manufacturing cost, reliable in work, high in propelling speed and low in noise, and is energy-saving and environment-friendly; and due to the simple structure, the loss in energy and power is reduced.