Abstract: This paper makes a calculation analysis on the seismic structure of gas tanks intended for the emergency diesel generators of a certain nuclear power plant with a finite element method. It describes the structural mechanics modeling process, the combination and use restrictions of static load and seismic load as well as the solving process of an earthquake response spectrum analysis method, and calculates the natural frequency and vibration mode of the structure and response under seismic loads. According to RCCM specification, it carries out assessment and strength verification of stress under various load combinations of gravity, internal pressure and earthquakes. The results show that the structural strength of the gas tank meets the specification requirements. Corresponding calculation and analysis methods have strong reference significance for the seismic structure design of gas tanks, worthy to be widely popularized in the actual produltion.