Ultrasonic vibration can reduce honing forces efficiently. As the honing wheel can be washed by ultrasonic cavitations of cooling liquid, its jams are decreased and the higher honing efficiency has obtained. Therefore, the combination of ultrasonic machining and gear honing is a method for gear fine machining with its wide application future. However, the gears with big diameter and thickness machined by ultrasonic honing are special loads, which influence the machining frequency of vibration system heavily. Hence, the horn and gear must be considered at the same time while designing the vibration system. In this paper, the frequency equations are derived according to stress match, wherein, the gear is considered as a thin disc and catenary horn is adopted. Then the influences of vibration of transformer that consists of horn and gear are investigated with the variety of the horn length and the machining frequency. The theoretical analysis shows that the resonance frequency of the horn and detune frequency of transformer have the different value. The results are proved by FEM, too.