The invention relates to an automobile water-cooling air compressor which is designed to solve the technical problem that the crank shaft oil supply structure and the venting and cooling effects of the existing similar air compressor are poor. The air compressor of the invention comprises a cylinder cover, a valve plate and a crank shaft box body, and has the design key points that the loop-type water cavity of the cylinder cover is matched with the loop-type groove of the valve plate to form a loop-type water-cooling path which is in the shape of the Arabic numeral eight, and aventing cavity is internally provided with a cooling radiating fin connected with the water-cooling path. The crank shaft is provided with a straightaway-type oil hole eccentrically along the axial direction, the straightaway-type oil hole is provided with at least three radial through holes, and at least one through hole is communicated with an oil inlet hole on the crank shaft box body; and a front bearing hole in the crank shaft box body is provided with a front sliding bearing, and a blank cap hole is connected with a blank cap which is provided with a rear bearing pedestal and an oil return path. The invention further lowers venting temperature, reduces the oil discharge amount of the air compressor along air, adopts the eccentric straightaway-type oil hole, has unimpeded oil path, low failure rate and stable operation and is suitable for serving as the structure improvement of similar air compressors.