Magnetic gears offer distinct advantages, including inherent overload protection and precise transmission ratio maintenance. Unlike conventional gearboxes, these non-contact transmission systems exhibit extended service lifetimes, making them particularly suitable for low-speed, high-torque applications. The operational principle of magnetic gears relies on magnetic field modulation, which generates rich harmonic components in the air gap magnetic field. Among these harmonics, the effective working harmonics play a crucial role in ensuring proper gear functionality. A typical magnetic gear configuration comprises three primary components: an inner rotor, an outer rotor, and a modulation rotor. The structural characteristics of these components significantly influence the harmonic content of the air gap magnetic field. This study focuses specifically on the impact of modulation rotor parameters on magnetic gear performance. Through systematic variation of the modulation rotor’s spatial distribution and width dimensions, we investigate corresponding changes in the electromagnetic characteristics. The analysis is conducted using two-dimensional finite element method simulations, providing detailed insights into the performance variations.