In order to improve the rationality of the tooth structure in the design process of double row planetary gear transmission, the structure and working principle of a certain type of Ravina gear transmission are analyzed, and the power transmission lines of each gear are defined at first. Secondly, the degree of freedom and transmission ratio of each gear are calculated, and the kinematic characteristics of the gear train are analyzed. At last, the assembly conditions of the planetary gear train are checked by adjacent conditions, concentric conditions and installation conditions. The results show that the tooth structure of each gear can meet the assembly conditions of the double row planetary gear train, and can realize the function of 7-speed transmission with motion determination and reasonable speed ratio.