Abstract: Rotary ultrasonic machining is an effective way for machining hard and fragile materials. In order to keep the machining reliable longer, thick electrode ultrasonic transducer should be used. Now relevant study is fewer. If needed, thick ultrasonic transducer is designed by both approximate calculation and test adjustment. In order to design the precise transducer, frequency equation of one-thick electrode ultrasonic transducer is induced .In order to verify the equation, both modal experiments and FEM are used, and the results show that：within the given thickness range of electrode, resonance fre-quency error is less than 5%, and the frequency can meet the engineering requirement.

Key words: Thick electrode, Frequency equation, Ultrasonic machining, Ultrasonic transducer