As an important basic component of humanoid robots, mechanical legs provide the robots with excellent manoeuvrability and versatility, which determine the core application performance such as job adaptability, walking speed, and load capacity. On this basis, the author summarize and study the design methods of the actuators and mechanical leg structures. Finally, some suggestions for the development of such robots in the future are mentioned. The motivation of this review is to provide useful guidance for future robotic designers to develop more efficient mechanical legs of humanoid biped robots. The synthesis of human motion is a complex procedure that involves accurate reconstruction of movement sequences, modelling of kinematics, dynamics and actuation, and characterization of reliable performance criteria.