A water-lubricated stern tube seal is a breathable water-lubricated stern tube seal device used in the ship industry for sealing the stern shaft tube of high-speed vessels. It includes a stern tube and a stern shaft seal, with the stern tube connected to the stern shaft seal at its front end. The stern shaft seal is equipped with an inlet, distinguishing itself by having an air vent at the top of the stern tube or the top of the stern shaft seal, which connects to an exhaust pipe. The beneficial effects of this utility model are: 1. By opening the exhaust pipe, air in the stern tube can be promptly discharged, preventing the formation of air pockets, ensuring smooth water flow through the stern tube with sufficient flow rate. This guarantees that the seals within the bearing and stern shaft seal are submerged in water, thereby avoiding overheating and burning of the stern shaft and the seal, enhancing the reliability and effective service life of the shafting system; 2. The structure is simple, and it can be implemented by simply opening an air vent at an appropriate location on the top of the existing stern shaft seal, with easy installation and maintenance.