A car cooling water pump comprises a water pump impeller, a mechanical seal, an O-shaped ring, a shell body, a shaft-connected bearing and a sprocket, wherein the mechanical seal is a wheel shaft seal of the water pump impeller, steel rings are arranged on the outer sides of a static ring and a movable ring of the mechanical seal, and intervals among the steel rings, the static ring and the movable ring are filled with magnetic liquid. As the magnetic liquid is arranged on the outer side of the static ring and the movable ring of the mechanical seal for sealing, the sealing effect of the car cooling water pump is better. The specific pressure needed on a sealing surface of the mechanical seal is half that in the prior art.