The invention discloses a vacuum paint spraying device for an air cylinder. The vacuum paint spraying device comprises a frame, an upper adjusting piece and a base, wherein first rails are arranged on the frame; a driving device is arranged on the upper adjusting piece; the air cylinder is arranged on the driving device; a mounting seat is arranged on the base; a connecting rod is arranged on the mounting seat; a spray nozzle is arranged on the connecting rod; a liquid chamber is arranged on the base; liquid water and a heating resistor are arranged in the liquid chamber; the vacuum paint spraying device further comprises an evacuating device. According to the scheme, the purpose of increasing the humidity of an entire working chamber is achieved through evaporation of the liquid water in the liquid chamber, and based on the feature that paint is insoluble in water, less paint sprayed from the spray nozzle is dispersed into the working chamber due to large humidity. Therefore, the surface the air cylinder can be covered with more than 80% of the paint spray from the spray nozzle, the utilization ratio of the paint is greatly improved, and paint waste is reduced.