Due to coupling of in-wheel motor and wheel/tire, the electric wheel system of in-wheel motor driven vehicle is different from tire suspension system of internal combustion engine vehicle both in the excitation source and structural dynamics. Therefore emerging dynamic issues of electric wheel arouse attention. Longitudinal vibration problem of electric wheel system in starting condition is studied in this paper. Vector control system of permanent magnet synchronous hub motor considering dead-time effect of the inverter is primarily built. Then coupled longitudinal-torsional vibration model of electric wheel system is established based on rigid ring model and dynamic tire/road interface. Inherent characteristics of this model are further analyzed. The vibration responses of electric wheel system are simulated by combining electromagnetic torque and the vibration model. The results indicate that abrupt changes of driving torque will cause transient vibration of electric wheel system. To be specific, vehicle body mainly undergoes longitudinal shake in 4Hz and unsprung mass suffers from longitudinal shock in 38Hz; the transient vibration of electric wheel system is most remarkable at zero velocity and decreases with vehicle speed. In addition, torque ripple will arouse 6pth order vibration, which is centralized in 40Hz and 100Hz and becomes noticeable in certain speed range due to resonance. The longitudinal vibration of electric wheel system in starting condition is highlighted and deserves attention. The detailed features and characteristics of this vibration are studied in this paper, which is favorable for design and analysis of in-wheel motor driven vehicle.