Abstract: The principal curvature radius of a ball screw pair was calculated using the structural parameters of the ball screw pair, and the curvilinear relationship between helix angle, contact angle, and principal curvature was plotted. Based on Hertz contact theory, contact deformation of the ball screw pair was calculated. Contact stiffness was then investigated using the relationship between contact angle, helix angle, and contact deformation. Calculated contact deformation values were verified with ANSYS FEM. The results demonstrated the validity of the theory. Contact characteristics of ball screw pairs can be effectively improved by increasing helix angle and contact angle.