The work aims to establish a mathematical model for calculating the profile and geometric characteristics specific to the profile design and optimization of screw compressor in large cold storage system, so as to provide theoretical basis for the profile design and optimization of screw compressor. With the widely used GHH profile as the research object, based on the geometric characteristic calculation method adopted, it was found that the sealing line of GHH profile was discontinuous. By replacing the arc-arc conjugate curve pair in the GHH profile with the arc-arc envelope conjugate curve pair, the continuity of the sealing line was achieved, and a modified GHH profile was proposed. Taking the modified GHH profile as the research object, the effect of profile parameters such as pitch radius of female rotor, inner radius of the male rotor and outer radius of the female rotor on the geometric characteristics of contact line, the meshing line and the blow hole was analyzed. The blow hole area was linearly positively correlated with the pitch radius of female rotor, the screw lead and the protection angle, and linearly negatively correlated with the inner radius of the male rotor and the outer radius of the female rotor and the radius of the elliptic arc. The outer radius of the female rotor had the greatest effect on the area of the blow hole. The area utilization rate decreased from 0.462 to 0.427, the length of the sealing line elevated from 174.5 to 182.3 mm and the blow hole area enlarged from 1.7 to 8.3 mm2 when the pitch radius of the female rotor increased from 48 to 60 mm. The established mathematical model for rapid calculation of geometric characteristics of rotor profile optimizes GHH profile, reduces leakage during rotor operation, improves theoretical Engine displacement, and provides theoretical guidance for rotor profile optimization.