<p>Ultrasonic vibration-assisted lapping is an advanced finishing technology that outperforms conventional lapping methods. It is capable of increasing the material removal rate, producing high-quality tooth flanks, and reducing noise in gear pairs. The design of the vibration system is one of the key enabling technologies for implementing the ultrasonic vibration-assisted lapping process. This paper presents a preliminary theoretical study on the design of the ultrasonic lapping vibration system for helical cylindrical gears. Based on wave propagation theory and Mindlin’s moderate thick plate theory, this study establishes a theoretical model of the ultrasonic lapping vibration system. It analyzes the dynamic characteristics of the combined horn and helical cylindrical gear assembly within the vibration system. A case study was performed to determine the resonant frequency and amplitude characteristics of the vibration system. Modal analysis and harmonic response analysis are performed using ANSYS. Finally, experimental validation is conducted via impedance analysis and vibration performance testing. The results show that compared to the design frequency, the relative deviations of the theoretical resonant frequency, finite element analysis frequency, and experimentally measured frequency are 0.15%, 0.98%, and 1.575%, respectively, all below 2%. Furthermore, the displacement amplitudes generated on the tooth surface of the helical cylindrical gear are highly similar, meeting the requirements for engineering applications. These findings provide a solid foundation for the industrial implementation of this finishing method for high-precision gears.</p>