Based on the mechanical characteristics of RC frame structures, using the seismic design scheme of adding rocking of moment frames. A 6-story RC frame was taken as the research object, the calculation model of the structure system was formed and the state space analysis method as well as pseudo excitation method are used to solve the stationary random response of the new structure system. The dynamic reliability of RC structure with different stiffness ratio rocking of moment frames under minor earthquake was discussed by using the dynamic reliability theory. The results show that the Conditional failure probability was decreased under minor earthquake both of the structure system and each floor of structure, and provides some reference to the engineering Design and research.