Mechanical knee joint capable of flexing when going back

The present invention relates to biomedical engineering technology, and is one mechanical knee joint capable of bending slightly during drawing back. The mechanical knee joint includes one ratchet wheel connected to artificial thigh, one lower connecting body connected to artificial calf, one ratchet connected through one disc spring to the lower connecting body and matched with the ratchet wheel, one grooved wheel rotated by the ratchet via the first wire, one main leg bending spring, etc. The present invention has double self locking to ensure the safety in use, automatic leg bending to result in natural pace and less impact of ground on the artificial limb, simple mechanical structure and other advantages.