A numerical solution for open resonators with slow varying section waveguides is presented in this paper. By using this method

when the profile of the longitudinal section of an open resonator is given

the field distributions

the resonance frequencies and the ra-diational Q values may be calculated. Calculations based on this method have also been made for an open resonator with conical waveguides

and the relationship among the resonance frequencies and the parameters of the resonators

and the relationship among the radiational Q values and the parameters of the resonators have been obtained.