Abstract: Objective To explore relationship between peri-implantitis and implant shape. Methods Three-dimensional finite element models of the implant and natural teeth were constructed, applying instantaneous force for 100 N in three directions including vertical, horizontal and oblique directions at 45°. The results of three-dimensional finite element analysis of implant and natural teeth were obtained by ANSYS workbench software. Results After bearing force for 100 N from vertical and horizontal directions, the maximum stress value that the implant applied to cancellous bone was much more than natural teeth, and was much more in the implant itself than the natural teeth. When bearing 100 N force from oblique direction at 45°, the maximum stress value produced by surrounding issue was between maximum stress value of vertical direction and horizontal direction, and it was the maximum value of implant in three directions. Conclusion In the perspective of shape, the thread-shaped implant is more likely to cause injury for cancellous bone than natural teeth when bearing the force from different directions. Therefore, the implant may easily lead to peri-implantitis than natural teeth, and cause failure of implantation.