Objective To simulate the tightening procedure of a cancellous lag screw by using the implicit dynamic analysis method, and to evaluate the stress distributions on the screw-bone interface. Methods Finite element models of a lag screw with the surrounding bone were developed, and the implicit solver was set up for implicit dynamic analysis on the tightening procedure of the lag screw. The mechanical properties of the screw-bone interface were also analyzed according to strain and stress distributions on the screw and the surrounding bone. Results The stress of the lag screw was mainly distributed in the proximal portion of the screw thread rod. The high-stress region of the bone around the screw was located outside the outer edge of the screw, and it was approximately equal to the depth of the thread. The area of high-stress distributions on the bone was the main region that resisted screw stripping. Conclusions The method of implicit dynamic analysis can accurately simulate the mechanical properties of the screw-bone interface during screw tightening. The discovery of high-stress distributions on the surrounding bone can help researchers to further understand and improve the stability of screw insertion.