Abstract: The smaller the volume of the pressurizer, the violent the change of the pressure and water level of the pressurizer caused by same surge flow in the transient condition of nuclear power plant. This phenomenon enhances the coupling of the pressure and the water level in pressurizer, and.causes the frequent action of the heaters and spray valves, and thus degrades the system stability or even results in unstable operation. Two-region non-equilibrium model of pressurizer is built using Matlab in this paper, and the coupling equation between main coolant system and pressurizer is derived. At last, the decoupled controller transfer function was calculated using the method of diagonal matrix, and the pressurizer decoupled controller is designed utilizing the frequency domain method.