Electric wheel systems of in-wheel motor driven vehicles consist of the motor controller, in-wheel motor and tire-suspension assembly. The coupling between the electromagnetic excitation and elastic structure gives rise to electromechanical dynamic issues. As for the structural layout of the electric wheel system, the driving motor is directly connected to the wheel without torsion dampers or transmission in the driveline, thus making the electric wheel structure a weak damping system. Moreover, the driving torque of electric wheel can change rapidly in various conditions of vehicle. As a result, the transient vibration problem becomes one of the key electromechanical dynamic issues in the electric wheel system. To investigate this problem, the electromechanical coupling model of the electric wheel system is established first. Then the transient responses of the electric wheel under abrupt changes of the driving torque are simulated. The results indicate that the tire mainly suffers from longitudinal shocks in the anti-phase rotational mode at 95 Hz and vibration in the in-phase rotational mode at 44Hz successively, while the motor vibrates in the in-phase rotational mode at 44Hz. As the electric wheel system is electromechanically coupled, the influence mechanism and rules of electromechanical parameters on the transient vibration are studied. The results show that the permanent magnet flux linkage increases damping ratio of the in-phase rotational mode in virtue of the electromagnetic stiffness and damping, thus further weakening transient vibration of motor. The anti-phase rotational mode is sensitive to tire’s stiffness. It is effective to optimize tire’s shock by adjusting tire’s stiffness. This paper reveals the electromechanical coupling mechanism of the electric wheel system, and provides reference for parameter design from the perspective of improvement in dynamic characteristics.