Mechanical seal for automotive engine cooling water pump, referred to as water seal, mainly composed of two parts: rotating ring and static ring. Static ring is installed in the pump shell, it is in static state in the actual use; dynamic ring is installed in bearing, it revolves with the bearing together in the actual use. The dynamic sealing medium is a pair of friction rings (dynamic ring, static ring), it preloads the sealing end through the bottom spring and provide axial pressure compensation.