Sagittal split ramus osteotomy (SSRO) is widely used as an excellent surgical technique with a wide range of indications for jaw deformities. However, regression after advancement of the mandible is considered problematic compared with that after setback. We constructed models of 5- and 10-mm advancement after SSRO, and performed mechanical analysis of changes over time in stress loading employing the 3-dimensional finite element method. Models of the mandible were prepared after SSRO using titanium plates and screws as osteosynthesis material after 5- and 10-mm advancement of the distal bone fragment. Occlusal force and the muscular strength of the closing muscles were applied to each model. The displacement was greater in the 10-mm model than in the 5-mm model with conventional and locking screw fixation, whereas it was smaller in the model with locking plate fixation than in that with conventional plate fixation. In addition, it was smaller in the model with 2-plate fixation than in the one with 1-plate fixation. 2-plate fixation with locking screws may be a useful bone fragment fixation method because the amount of advancement increases, leading to postoperative stability. (J Osaka Dent Univ 2021; 55: 99-111)