It is difficult to mathematically describe the metamorphic process of gearshift and identify its own transmission characteristics of planetary shifting mechanism. Therefore, the metamorphic theory was interpreted aiming at planetary shifting mechanism firstly. Based on the mechanism conversion method, the constraint function, which described the dynamics traits of kinematic pair between two adjacent parts was transformed into the space of relevant revolving speed. And its transformation rule was defined. The adjacent matrixes of components and their each correlation was constructed aiming at planetary shifting mechanism, whose elements were constraint functions. And according to the operation logic rule of gear shift by operating clutch and brake, the metamorphic function of shifting configuration evolution was separately deduced based on configuration adjacent matrix. The principle of configuration evolution was revealed with an example to be analyzed. The identification formula of special configurations, including neutral position and direct position were established. After the construction of relative speed functions and the identification of characteristics parameters, the automatic identification method of system transmission ratio and torque function was presented based on configuration metamorphic function eventually. It was used to automatically analyze the transmission characteristics of planetary shifting mechanism. The application of this method wasdiscussed aiming at the planetary shifting mechanism of one tractor. It was indicated that this method was feasible and effective. And it supplied the theory references for computer innovative design of the vehicle power train. 