A model selection method and new principle for servo motor and reducer of casting machine was put forward, which was based on continuous movement and on account of the shortcomings of traditional selection method, such as enormous computation and poor applicability. By using the graphic expression, the method manages to judge the feasibility of alternative motors and reducers expediently, and then makes optimization towards the rest of motors and reducers. Through comparison examples, it was concluded that new method, compared with the traditional method, has the merits of simple, intuitive, and good effect in practice. It can be widely applied in all servo motor and reducer selection of continuous motion.