Abstract: The pressurizer is a primary equipment of the reactor coolant system.Its main function is to control the pressure of the reactor coolant system.The pressurizer is classified Safety class 1,RCC-M class 1,Seismic class 1.The aseismatic capability of the pressurizer should be evaluated through two facets.One is that the nature vibration frequencies should be sufficiently removed from the excitation frequencies for which accelerations are significant.The other is that the stress of pressurizer under seismic load is lower than allowable stress.Seismic analysis of pressurizer is performed in normal operation condition and initial reactor start-up condition via finite element methods.