Abstract: The analysis uses the mode-matching technique to generate a parameter matrix which can be cascaded for computing the resonant frequency and Q value of a complex cavity consisting of a series of waveguide sections is introduced. Program was designed to calculate the parameter matrix to get the eigenvalue parameters of a cavity. The result indicates that the simulation results of an input cavity obtained by the program are in good agreement with the cold-test results. The analysis provides useful information for further study of beam-wave interaction and design of gyrotrons.