With the development of industry, higher requirements for the load sharing and dynamic load factor of planetary transmission system have been put forward. On the basis of traditional ring gear structure, thin-walled ring gear, new material ring gear and elastic support ring gear have been designed and applied. However, the structural characteristics and flexibility differences of each ring and their influence on the system load sharing and dynamic load factor have been rarely reported in the literature, resulting in the blind spot in the design and selection of the system components. In this paper, by establishing the finite element models of each ring structure, the structural characteristics and flexibility differences of each ring were compared and analyzed. Combined with the dynamic model of planetary transmission system, the differences of the system's load sharing and dynamic load factor under different structures were obtained when the system errors were considered. The analysis shows that the flexibility of the traditional ring gear is the worst, and the system's load sharing and dynamic load factor are obviously larger than those of the flexible ring gear. The thin-walled flexible ring gear has the best load-sharing effect and the fluctuation is smooth, but the dynamic load factor fluctuation of each branch of the system increases. Due to the structural characteristics of the elastic-pin ring gear, the comprehensive time-varying meshing stiffness fluctuates violently, and the stiffness increases obviously when it is at the pin position. Although the load sharing of the system is reduced, it is chaotic and the dynamic load factor of the system is obviously enhanced.