Objective To explore the muscle force characteristics of the knee joint during a Taekwondo roundhouse kick in Korea. Methods Kinematic and dynamic data from twelve elite Taekwondo athletes were collected using the DaeDo electronic scoring system, Vicon optical motion capture system, Kistler three-dimensional force plates. The OpenSim software was used to simulate these movements and calculate the muscle forces, joint torques, joint stiffness, and muscle coordination patterns of the knee. Results During the knee-lifting and striking phases, the coronal torque of the knee joint in the attacking leg was significant, and the sagittal torque peaked during the strike. For the supporting leg, the highest coronal torque of the knee joint occurred during knee lifting, with the sagittal torque reaching its peak during strike. In terms of muscle activity, the semimembranosus and long head of the biceps femoris in the attacking leg exerted greater force during the striking phase, whereas the semimembranosus and medial head of the gastrocnemius in the supporting leg were more active during the recovery phase. Five muscle synergy patterns were observed during the Taekwondo roundhouse kick. Conclusions Significant differences were found in the muscle forces and knee joint torques of the attacking and supporting legs when athletes performed the roundhouse kick, and there was a complex muscle synergy.