The invention relates to a mechanical prosthetic arm. The mechanical prosthetic arm is composed of a hand, a wrist, a forearm, an elbow joint, an upper arm and a shoulder joint, the hand is composed of a palm part and finger parts, the front end of the wrist is connected with the palm of the hand through a wrist disc, the tail end of the wrist is connected with the forearm through a forearm driving mechanism, one end of the elbow joint is connected with the forearm, the other end of the elbow joint is connected with the upper arm, the upper arm is installed on a body through the shoulder joint, and the mechanical prosthetic arm is provided with a finger driving mechanism, a wrist driving mechanism, the forearm driving mechanism, an elbow joint driving mechanism and an upper arm driving mechanism. Multi-degree-of-freedom movement of the arm is realized, and the mechanical prosthetic arm is of a pure mechanical structure and is reliable in structure; and the fingers adopt connecting rodmechanisms and thus are reliable in structure, grasping intensity is large, and the whole arm adopts multi-degree-of-freedom design, and can overall realize the flexible and quick response effect.