A method of controlling a vehicle driving system having differential gear including an input shaft, an outlet shaft and a reactionary shaft, a flywheel, an engine, the flywheel and the engine being interlocked with the input shaft, an output shaft interlocked with the outlet shaft, a first motor generator (MG) interlocked with the reactionary shaft and a second MG adapted to receive the output electric power of the first MG as input. If the indicated torque of the output shaft as indicated by the pedaled quantity of the accelerator pedal is T2 and a torque of the reactionary shaft is Trd, while a power transmission efficiency from the input shaft to the reactionary shaft by way of the differential gear, a power transmission efficiency from the input shaft to the output shaft by way of the differential gear and a power transmission efficiency from the reactionary shaft to the output shaft by way of the first MG and the second MG are respectively .eta.mr, .eta.mo and .eta.e, a critical speed ratio of the differential gear, a rotational speed of the output shaft and that of the flywheel are respectively ec, N2 and Nf, the torque Trd is determined by the relation of Trd=(ec-1).times.T2.times..eta.mr/[{.eta.mo-(.eta.mr.times..eta.e)}+{(ec.- times.Nf/N2).times..eta.mr.times..eta.e}] and generation of electric power of the first MG is controlled so as to cause the reactionary shaft to produce the torque Trd.