During physical exercise, the knee is vulnerable to injuries. In order to prevent such injuries, many people have analyzed knee pads and sports biomechanics of knee. This paper studies the simulation model of knee joint motion. On the basis of analysis on the geometric model of the knee joint during exercise, it establishes the dynamic equations of knee joint motion and obtains the mechanics response function of knee joint muscle, discusses the change trends of the angle and the angular velocity over time by biomechanical simulation data of knee joints and related systems in the starting process, verifies the reliability of the model through the simulation results, and provides a theoretical basis for medicine and sports to prevent damage.