Objective Revealing the effect of exercise posture on joint function is of positive significance for in-depth understanding of the mechanism of knee pain. This study investigated the influence of Tai Chi exercise posture on knee joint load and the strategy of coordinated muscle contraction.Method recruited 20 Tai Chi practitioners with more than 3 years of Tai Chi practice, using Qualisys high-speed motion capture system and AMTI BP400600 three-dimensional force plate, collected adduction angle, tibial angle, joint force, joint torque and of the supporting leg of the "The step lunge" movement, and obtained the quadriceps and gastrocnemius muscle strength through Lifemod simulation software. The muscle strength performance, recruitment mode and activation method of Baseline gait, Toe-out gait and Toe-in gait were compared.Results The tibial angle and adduction force increased in the Toe-out gait but the Toe-in gait remained unchanged; the strength of the medial femoris, Semimembranosus, semitendinosus and lateral gastrocnemius muscle increased in the Toe-out step; the external femoral muscle and medial gastrocnemius muscle increased in the Toe-in step,The gastrocnemius muscle is preferentially activated than the quadriceps muscle, and the way of muscle recruitment changes. Conclusion Prioritizing the activation of the gastrocnemius is the basic feature of the lower limb muscle activity in Tai Chi movements. The role of the gastrocnemius may not be compensation, but lead. The way of movement of the ankle joint may be one of the reasons that triggers the preferential activation of the gastrocnemius muscle. Tai Chi exercise posture changes the way of muscle force recruitment and affects knee joint function. Standardized movements can be used as a reference for osteoarthritis exercise therapy and have clinical application significance.