By comparing the biomechanical characteristics of lower limbs of young people with different body mass index before and after the intervention of Baduanjin, the aim is to provide reference for scientific exercise prescription of young people with different body mass index. Methods: The BTS SMART 3D infrared motion capture system was used to capture the motion parameters, the KISTLER force measuring platform was used to collect the dynamic parameters in real time, the Anybody simulation software was used to calculate the kinematic parameters and dynamic parameters, and BTS SMART Analyzer was used to compare the different integral electromyography values. Results: (1) There was no significant difference in the indicators before the intervention of Baduanjin. After the intervention significantly increased the angle and angular velocity of the knee joint in the extension and flexion of the standard group,overweight group and obesity group(P<0.05), and significantly increased the angular acceleration of the knee joint in the extension and flexion of the standard group(P<0.05). (2) Baduanjin significantly increased the knee flexion force and moment(P<0.05) in the standard group,overweight group and obesity group, and increased the hip flexion force and moment(P<0.05) and ankle metatarsal flexion force and moment(P<0.05) in the standard group. Compared with the obesity group, knee flexion force and moment in the intervention standard group were significantly different(P<0.05), knee joint force and moment were positively correlated with BMI (r=0.92, 0.91). (3) Baduanjin significantly increased the muscle strength of iliopsoas, gluteus medius, piriformis, gluteus maximus, rectus femoris, sartorius, tibialis anterior, biceps femoris longhead, flexor digitorum longus, flexor pollicis longus, musculus peroneus longus and musculus peroneus brevis(P<0.05). (4) Baduanjin significantly increased the iEMG of rectus femoris, tibialis anterior, biceps femoris (P<0.05). Conclusions: Baduanjin can improve the muscle strength and neuromuscular control ability of young people. The greater the BMI, the greater the flexion force and moment of knee joint.