The loss of upper limb function brings a lot of inconvenience to the life of amputees. In order to improve the life quality of upper limb amputees, it is necessary to develop a low-cost, lightweight and powerful prosthetic system. In this paper, a three-degree-of-freedom modular light-weight upper limb prosthetic arm and its multi-joint cooperative control system are designed to provide a lightweight, economical, modular and comprehensive prosthetic solution. By using the hollow structure design, the overall weight of the prosthetic arm is significantly reduced (about 2 kg), which is much lower than existing commercial prosthetic products, while ensuring the number of degrees of freedom and effectively reducing manufacturing costs, improving the comfort and suitability of the prosthetic arm. In addition, the multi-joint control system designed in this paper, combined with the precise coordination algorithm, can accurately control each joint to reach a predetermined Angle at the same time, to meet the needs of different degrees of amputees for multi-joint cooperative movement. Through precision and efficiency tests, the results show that the prosthesis performs well in terms of control accuracy, and the motion efficiency can meet most of the needs of daily life.