Abstract: To research the buffering effect of secondary supports in reactor vessel internals under the assumption accident of core drop (core barrel broken down), a buffering effect analysis of secondary supports is performed, based on the technology of water buffering and mechanical buffering. In this paper,  the process for core drop is numerically modeled, and  the core barrel movement mechanism under different vertical gap, coolant temperature and initial flow rate is analyzed based on Fluent. The impact process in the end of core drop is analyzed and the water buffering effect of the secondary support is studied based on LS-DYNA. The analysis results show that, using the technology of water buffering and mechanical buffering, the secondary supports can bearing the impact energy of the core drop, and the coolant can buffer most of the impact energy. The buffering effect of secondary supports in this paper is better than that of the traditional support structure, to ensure the integrity of the reactor pressure vessel (RPV).