In this article, the method of relating the dimensional parameters of the klystron tube resonator cavity to one of its parameters and then analyzing the cavity using this parameter is discussed. This new method makes it much easier to design and optimize the resonator. This method has been used to design a cavity for 3GHz frequency, so that after specifying a general parameter of the cavity and making other dimensions depend on it, and then using the sweep of this geometric parameter to check the changes in the electrical parameters of the design of the RF section including the resonance frequency , M and R/Q and then the effects on the output efficiency of the klystron tube has been studied using Mathematica and Microwave Studio CST software.