A remanufacturing system based on robot MAG surfacing has been developed recently. In this paper, the work principle, functions and composition of this system are introduced. A worn metal part to be remanufactured should be preprocessed firstly, and the defective model of the part gained by reversing engineering technology is compared with normal model of the metal part, then the prototyping path layout is carried out combined with MAG welding process, finally the remanufacturing prototyping is implemented. The remanufacturing system is composed of robotic system (as executing machine), 3D laser scanner (as reversing scanning device), digital pulse MAG welding power source (as prototyping equipment), desk computer (as central control unit) and software modules that support various functions. The functions of the remanufacturing system comprise calibration of system, part reversing measurement, data processing, defective model reconstruction, welding remanufacturing prototyping path layout and etc. It is indicated that the exploitation of the remanufacturing system will provide an effective way for the remanufacturing of metal defective parts.