The present disclosure discloses a knee joint power generation device based on bidirectional ball screw drive, and belongs to the field of biomechanical energy harvesting. The power generation device converts the rotary motion of the knee joint during human movement into a linear motion of the rope by the rope driving device, and then converts the linear motion into a rotary motion through a bidirectional ball screw to directly act on the motor, thereby converting the human biological energy into electric energy in the whole process to achieve power generation. The power generation device of the disclosure can meet the requirements of normal power generation during high-speed running and low-speed walking, has long-term high-efficiency and stable performance, can be easily worn on different people, has light overall weight and costs less loss of human walking metabolism.