Objective: To investigate the impact of overweight and obesity on knee joint biomechanics during running in children and to provide theoretical support for scientific exercise prescription and reduced risk of exercise injury in overweight and obese children. Methods: Fifteen children aged 7-11 years old with normal weight (healthy group) and overweight/obesity (overweight/obesity group) were selected from June to August 2020. Participants ran through the force measuring platform at a speed of [3.5×(1-5%)~3.5×(1+5%)]m/s. The kinematic and dynamic data of the knee joint were collected simultaneously by the Simi Motion motion capture system and the Kistler three dimensional force measuring platform, and the surface area and density of the tibial plateau were measured by peripheral quantitative computed tomography. The difference of knee joint angle, impact mechanics and knee joint torque based on tibial plateau dimension were compared between the two groups. Results: The knee abduction peak angle of the overweight/obesity group[(6.14±4.16)°] was higher than that of the healthy group[(2.57±1.36)°] ( t=-3.16, P < 0.05 ). Based on the standardization of tibial plateau dimension, the impact mechanics (peak vertical ground reaction force, peak impact force, maximum load rate and average load rate) and knee joint torque (knee flexion, extension, adduction peak torque) in the overweight/ obesity group were higher than those in the healthy group ( t=-4.26, -4.52, -2.97, -2.74, -2.17, -4.27, -3.70, P <0.05). Conclusion Overweight/obese children show abnormal running mechanics and knee joint load. Higher joint load may indicate increased risk of anterior cruciate ligament injury among overweight/obese children.