To provide a method for operating an electric machine in a hybrid electric vehicle for high-dimensionally balancing the torque response stability, fuel economy and engine emission property of a vehicle.

This method for operating an electric machine includes: a step (61) for determining the magnitude of a driving power requested by a driver; steps (50, 52) for determining the lower limit/upper limit of the engine driving power of an engine within a prescribed time after the request of the request driving power; steps (64, 72) for determining the lower limit/upper limit of the electric driving power of the electric machine; steps (62, 70, 74, and 76) for using the magnitude of the request driving power, the lower limit/upper limit of the engine driving power, and the lower limit value/upper limit of the electric driving power in order to determine the assist upper limit/lower limit of electric assist so that a requested request driving power can be generated within a prescribed time; and a step (82) for operating the electric machine so as to provide the electric assist between the assist upper limit/lower limit.