This paper conducts a systematic study on the suppression of common-mode voltage in permanent magnet synchronous motors for electric aircraft propulsion systems. First, by establishing a correlation model between winding structure parameters and common-mode voltage, the interaction mechanism between the two is deeply analyzed. Next, based on the theory of air-gap magnetic field harmonic decomposition, the quantitative mapping relationship between each harmonic and common-mode voltage is revealed. Then, using a 10-pole/12-slot surface-mounted permanent magnet synchronous motor (SPMSM) as the research object, a new method for adjusting the common-mode voltage amplitude-frequency characteristics through optimized winding arrangement is proposed. Finally, an active common-mode voltage suppression method based on coil distribution adjustment is designed. Finite element simulation results show that the proposed method can effectively reduce common-mode voltage, providing important theoretical basis and technical support for electromagnetic compatibility design in electric aircraft propulsion systems.