Objective Bone screws are one of the most widely used internal fixation implants in orthopedics. As they have to be implanted into human body for a long time during treatment, it is essential to evaluate their mechanical safety before clinical use. Insertion torque is the most important mechanical index of medical bone screws, therefore to establish a scientific calculation model of the torque is of great significance for the development and clinical application of bone screws. Method This paper builds the mechanical calculation model for the screw forming stage with simulation carried out in computer according to the three stages of the screw insertion process for the self-tapping screw. Meanwhile, we perform the insertional experiments of screws with specification of φ2.9×12 from three manufactures on polyurethane test blocks of different grades according to ASTM F543-17(YY/T 1506-2016), and the results are compared with the calculated ones. Results The deviations between the insertion torque predicted by the model and the value measured in the experiments are 0.005N·m and 0.012N·m within the acceptable error range, which are less than 10% of the average value of the experimentally measured ones. Conclusion The mechanical calculation model can be used to simulate and predict the insertion torque of medical bone screws in research and development or clinical use, and its combination with invitro mechanical experiments can be helpful in developing and designing bone screws.