Objective To evaluate biomechanical properties of a S 1 pedicle screw and rod-plate internal fixation developed by author for fixation of vertically unstable pelvic fracture and therefore to provide scientific foundations before clinical application. Methods Twenty fresh frozen cadavaric pelvis were used to create C 1-3 pelvic fracture (Tile classification). The fracture was fixed by using S 1 pedicle screws and rod-plate internal fixation, S 1 pedicle screw and Galveston technique, transiliac rod fixation, iliosacral screw fixation, and reconstruction plate, respectively. The mechanical stability of these five different internal fixation approaches was compared by using stress analysis method. Results Under the same load condition, the strength, rigidity and stability of S 1 pedicle screw and rod-plate internal fixation showed significantly better results than other methods and there was no statistical difference when compared with the result of intact control ( P <0.05). Conclusion S1 pedicle screw and rod-plate internal fixation was a better internal fixation approach as compared with other tested ones, which implied a new fixation method for potential clinical application.