Objective To probe into biomechanical evaluation on changes of time and space, kinematics and dynamics before and after surgeries by using three-dimensional gait analysis. Methods Retrospective analysis was conducted on 11 patients with knee osteoarthritis of medial compartment type admitted to our department between Sep. 2016 and Dec. 2018 and treated by Ilizarov external fixation technique of minimally invasive bone cutting at lower proximal tibia. There were 21 knees in total (10 cases of both knees) with the major symptom of pain in medial knees and history of conservative treatment for more than 2 years. According to clinical practice, follow-up was conducted after corresponding treatment and disposal. The gait parameters of space-time, kinematics and dynamics were recorded in the cycle of three time points: pre-operation, postoperative demolition of external fixators and follow-up at postoperative six months. Then, three-dimensional gait data was analyzed and compared. Results All patients were received 6 to 23 months’ follow-up, with an average of 12.7 months and external fixators were dismantled after 14.8 months on average. Gait analysis and comparison were carried out at three time points of pre-operation, postoperative demolition of external fixators and postoperative half year and there was no significant difference in step speed and stride parameters of time and space (P > 0.05). Kinematics parameters of knee flexion angle gradually improved. Varus and valgus were gradually corrected (P < 0.05). While, the range of ankle motion activity had no obvious difference when demolishing external fixators compared with pre-operation (P > 0.05), and the angle of ankle valgus has increased considerably (P < 0.05). When following up for 6 months, the range of ankle motion increased greatly and had obvious difference compared with pre-operation and the time of demolishing external fixators (P < 0.05). The angle of ankle valgus increased considerably compared with pre-operation (P < 0.05), while the change was not obvious compared with the demolition of the external fixator (P > 0.05). In dynamic tests, postoperative varus torque of knee joint and the angle of knee adduction impulse gradually decreased (P < 0.05). Compared with pre-operation, When demolishing external fixators, ankle valgus moment increased, plantar center pressure trajectory had obviously lateral migration (P < 0.05), while postoperative follow-up for six months compared with the demolition of the external fixators had no obvious difference (P > 0.05). Conclusion Ilizarov external fixation technique of minimally invasive bone cutting at lower proximal tibia to treat patients with knee osteoarthritis meets the demands of biomechanics. And gait analysis tests can accurately assess the clinical efficacy of this therapeutic technique.