Aiming at comparing the pre-operative and post-operative gait characteristics and therefore establishing post-operative rehabilitation guidance for patients with end-stage knee osteoarthritis (KOA) merged with varus deformity, this study captured the level walking and sit-to-stand trials of 9 patients with 3-dimensional motion analysis system and after which musculoskeletal multi-body dynamic analysis was conducted. The study indicated that the average range of motion (ROM) of the proposed-surgical knee was 24.4°–57.6° and that of the non-surgical knee was 22.5°–71.5°. The knee ROM of control group during level walking was 7.2°–62.4°. When the unilateral KOA patients stood up from chair to complete the sit-to-stand movement, the ground reaction forces (GRFs) symmetry was 0.72–0.85, which means that the non-surgical limb bear the majority of body weight. The GRFs of the bilateral KOA patients were smallest during the sit-to-stand movement. The strategy that the non-surgical limb dominates in loading bearing taken by the unilateral KOA patients to cover most post-operative daily activities could increase the risk of KOA among non-surgical side joints as a result of long-term excessive loading-bearing. The study, on kinematics and biomechanical characteristics of patients with KOA merged with varus deformity, could help to understand the pathogenesis of KOA merged with varus deformity from the perspective of biomechanics and to provide strong clinic guidance for the pre-operative evaluation, prevention and post-operative recovery for patients.