Abstract: Based on the basic theoretical model of nitrogen-typed pressurizer,this paper analyzed the steady and transient characteristics of the pressurizer,and the variations of the pressure,water level,water enthalpy,water mass,nitrogen temperature,nitrogen volume with the change of time are predicted using the model under two different fluctuation flow rate.It is found that,when fluctuating flow is positive,the pressure,water region mass,enthalpy,water level and nitrogen temperature all increase,while nitrogen volume decreases.When fluctuating flow is negative,the characters of nitrogen-typed pressurizer are opposite.In addition,the time response of nitrogen-typed pressurizer is very good.Furthermore,the effects on the steady and transient characteristics of main parameters as well as the experimental verification should be carried out in the future.