Abstract: Seismic analysis is one of most important parts of fast breeder reactor core design. It is necessary for structural integrity assessment and analysis of variation of reactivity under the earthquake. Moreover some important data for qualification of the scram capability of the control rods during the earthquake could be provided. In this paper, FINAS, one finite element code developed by Japanese engineers, was used. The calculation model and method was studied on one single assembly in China Experimental Fast Reactor (CEFR), as an example. Some preliminary analyses including modal analysis, free vibration analysis and analysis of shock against rigid wall were carried out, which prepares for the seismic analysis on multiple assemblies in FBR core.