Abstract: To mitigate the significant torque ripple in interior permanent magnet synchronous motors （IPMSM）, this paper proposes a rotor topology with auxiliary slots, based on the principle of air-gap magnetic field modulation. First, a mathematical model of the motor is established, including analytical expressions for its electromagnetic performance. This is followed by an analysis of the mechanism behind torque pulsation generation and its influence on motor operation. Secondly, a parametric model of the motor is developed using a finite element analysis platform. Subsequently, combined with parameter sensitivity analysis, a hierarchical optimization strategy is proposed: high-sensitivity parameters are optimized using a multi-objective genetic algorithm, whereas low-sensitivity parameters are refined through a scanning method. This approach optimizes the topological parameters of both the stator and rotor, leading to an optimal parameter solution. Finally, a comparative analysis of the electromagnetic performance of the motor before and after optimization was conducted. The results demonstrate a significant improvement following optimization: the cogging torque was reduced by 91.6%, the torque ripple decreased by 74.7%, and the third harmonic of the no-load back electromotive force was reduced by 75.3%. These enhancements effectively suppress torque pulsation and contribute to overall improved motor performance.