Abstract: Water-lubricated single screw air compressor is lubricated and sealed by injecting water into the working chamber. A mathematical model of the working process of a water-lubricated single-screw air compressor was established in this study. The influences of the diameter of the water injection aperture and rotation speed on compressor performance was analyzed through the model. Weber number was introduced to evaluate and analyze the atomization effect. Results show that the discharge temperature is effectively reduced by increasing the diameter of the water injection aperture, resulting in the compression process of the compressor moving towards an isothermal state. Under rated conditions, the increase in the diameter of the water injection aperture from 5 mm to 7 mm reduced the discharge temperature of the compressor, improved the volume efficiency, and the adiabatic efficiency by 40.4 K, 3.99%, and 7.57%, respectively. Although the increase in rotation improved the efficiency of the compressor, there was a decrease in the cooling and sealing effect due to a reduction in the water-air ratio. Therefore, the impact of an increase in speed on the efficiency of the compressor was gradually weakened. With the increase of the diameter of the water injection aperture, the average diameter of atomized droplet increased. The minimum water flow rate corresponding to different water injection apertures was determined according to Weber number.