Abstract: The complete finite element model of reactor inernals of a certain type test reactor including grid plate assembly and core component is established. Modal combination method of CQC is adopted for the spectrum analysis of the reactor internals. Effect of added mass in still water on the transverse vibration characteristics of the reactor core is considered, but the effect of the added mass of water on the axial direction is ignored. Then two finite element models are established: one is the approximate model of the reactor internal in the water, which is used for spectrum analysis of structure under transverse earthquake load. Another is the model of the reactor internal in the air, which is used for the spectrum analysis under axial direction earthquake load and static analysis under gravity. The results show that the reactor internals are in compliance with the requirements of ASME codes.