Due to the double action of road excitation and vehicle weight, the stator and rotor of the in-wheel motor (IWM) for electric vehicles (EVs) are relatively eccentric, thus generating an unbalanced magnetic force (UMF). When the vertical component of UMF is coupled with the vertical vibration of the suspension system of the vehicle, the ride comfort and other properties of EV are affected. To study this electromechanical coupling problem, by taking a permanent magnet IWM as the research object, the vertical dynamic characteristics of electromechanical coupling of an IWM drive system for electric vehicle were investigated. Firstly, the air gap flux density distribution of IWM under load was obtained by superposition method of magnetic field. By introducing complex relative permeance and correction coefficient of permeance when the motor was eccentric, analytical models of the eccentric magnetic fields of IWM and UMF were obtained with the stator slotting effect taken into account, and the validity of the analytical models was verified by finite element simulation and prototype test. Then, according to the real-time coupling relationship between the vertical vibration of the suspension system and the eccentric UMF of IWM, the dynamic equation of the vehicle was solved by using the Lagrangian method, and the vertical coupling vibration model of a quarter car body was established. Finally, taking the vertical vibration acceleration of the stator of IWM, the vertical vibration acceleration of the car body, the dynamic deflection of the suspension and the dynamic load of the tire as the main indexes, the effect of electromechanical coupling on the vertical dynamic characteristics of EV was studied, and the mechanism of electromechanical coupling between the output characteristics of UMF and dynamic response of EV was revealed. The results show that the electromechanical coupling effect impairs the ride stability, operation stability and safety of EV.