A new type of transducer for ultrasonic assisted-lapping of spiral bevel gear is produced based on a four-section composite horn and sandwich piezoelectric ceramic transducer. First, the frequency equation of the ultrasonic lapping transducer is derived according to Newton's law and the theory of the ultrasonic transmission line. Second, the structural parameters of the transducer are determined with the resonant frequency, vibration mode and the input power of piezoelectric ceramics. Then, the acoustic and structural parameters are modified by the equivalent acoustic parameter correction method and the mass reciprocity method. Furthermore, the modal analysis and harmonic response analysis are carried out in ANSYS, by which the resonant frequency, vibration amplitude, vibration speed ratio and admittance of the transducer are deeply studied. Finally, the impedance characteristic test and vibration characteristic experiments are carried out. The ultrasonic-lapping performance of the composite structure lapping transducer is confirmed by the ultrasonic lapping experiments of 5 pairs of spiral bevel gears.