For the dental implant which is available in various dimensions and/or configurations, the dynamic testing should be performed under "worst-case" condition. Thus, a finite element analysis was applied to investigate the effect of implant diameter and length on the stress distribution of dental implant and find out the worst-case condition. In this paper, six models were computer-simulated by varying the implant diameters (3.5, 4.3 and 5.0mm) and lengths (8 and 15mm). The models were used to investigate the influence of length factor: (1) implants with a diameter of 3.5mm and lengths of 8mm and 15mm; (2) implant diameters of 4.3mm and lengths of 8mm and 15mm; (3) implant diameters of 5.0mm and lengths of 8mm and 15mm. The influence of implant diameters was modeled using implant with a length of 8mm and diameter of 3.5, 4.3 and 5.0mm, length of 15mm and diameter of 3.5, 4.3 and 5.0mm. One vertical load (200N) was applied on the horizontal plane of the crown. A pre-torque of 30N• cm on the central screw was loaded to simulated pretightening force. The results showed that the maximum stress () of each component occurred in the model with the longest implant length and smallest diameter (model 2).