Objective To compare the biomechanical stability of different fixation methods for unstable pelvic fractures, so as to provide references for clinical treatment. Methods An unstable pelvic fracture model (Tile C) with the sacroiliac joint dislocation at one side and the pubic rami fracture was constructed via three-dimensional finite element method. In the front of the pelvis, the fracture models were fixed with anterior pelvic Stoppa approach (ASA),subcutaneous anterior pelvic approach (APA), anterior pelvic ilioinguinal approach (AIA) and anterior pelvic external fixation (AEF),and the rear was fixed with sacroiliac joint screw (SIJS）and posterior tension-band plate (PTP). The Von Mises stress and strain distributions of fracture models fixed by different combinations of fixation approaches were analyzed under simulated standing conditions. Results After the models were applied with 500 N vertical load, the maximum stresses at the fracture sites were all reduced, which were smaller than 10 MPa in the front of the pelvis. The maximum stress at the anterior and posterior part of implants in sequence was ASA＜AIA＜AEF＜APA, and the average displacement under the same stress in sequence was ASA＜AIA＜AEF＜APA. Meanwhile, the maximum stresses at the sacroiliac joint and the posterior part of implants in PTP group were significant smaller than those in SIJS group, and the maximum total displacement and vertical displacement in PTP group were also smaller than those in SIJS group. Conclusions Unstable pelvic fractures could be significantly improved when the fracture was fixed by implants in eight combined methods. However, the overall biomechanical properties of the AIA groups were superior to those of the AEF groups and the APA groups. The stability of PTP groups in the treatment of posterior injury was better than that of SIJS groups.