Different movement patterns of fencing project are conducted through the right and left limbs, whose unique lunge attack defensive pace and great impact in the moment of the swing leg are considered as the main reasons to cause the swinging leg knee joint injury. How to reduce the injuries in knee lunge action has been a focus of research institutions at home and abroad. The application of sports biomechanics was analyzed in sports based on this. The biomechanical index of the National Women's epee reserve players lunge were tested considering fencing as an example, which was compared with dynamics index of no initial velocity falls naturally from 60 cm platform. Knee joint angle, ground reaction forces, knee joint torque and reaction force changes in the lunge movement of athletes were studied, and the causes of knee joint injury was analyzed. Practice has proved that the research of knee biomechanics mechanism of International Women's epee fencing lunge movement can improve the training effect and prevent sports injury effectively.