Based on the surgical program of the combined proximal tibial osteotomy (CPTO) to treat varus knee osteoarthritis, the biomechanical properties of two common internal fixation systems in CPTO with finite element analysis were studied. The three-dimentional finite element model of proximal tibial osteotomy combined with Tomofix and Tomofix-Asian internal fixation systems were established, the knee joint stiffness, wedge displacement and the stress distribution of tibia and implants were compared. The results show that the stiffness and the average wedge displacement increase by 23.8% and -85.5% respectively, using Tomofix-Asian internal fixation system compared with Tomofix internal fixation system. The average stress on tibia decreases by 36.5%, and the maximum stresses on plate and screw increase by 16.6% and 4.6%, respectively. Therefore, the Tomofix-Asian internal fixation system usage during CPTO can improve the knee joint stability, reduce the wedge displacement, and provide strong support for bone healing. However, the obvious decrease of bone stress due to the high-strength support of the internal fixation system may increase the risk of stress shielding effect leading to osteoporosis.