It is two main factors that the refrigerant leakes and preheated in compress process for the discharging of the screw refrigeration compressor. The size of them directly is related to the form of the screw and the precision of the screw processed, and the screw cooled etc. Each compressor factory is different from others for designing and processing the screw. In the engineering design, it is difficult to calculate volumetric flow rate of the screw refrigeration compressor. The main factor of the volumetric flow rate is analyzed for the screw refrigeration compressor. A method of calculating the volumetric flow rate is inferred and checked. It can be for the use of engineering design