Abstract: The present invention relates to a hybrid power-generating device and a power generating method thereof. The hybrid power-generating device is primarily comprised of: a primary electrical generator and an auxiliary electrical generator with different characteristics, both mechanically coupled to a prime while enabling the rated power of the auxiliary electrical generator to be smaller than that of the primary electrical generator; wherein, as the prime is operating at a low rotation speed or at its initial operating stage, the auxiliary electrical generator is enabled to be driven and activated thereby; and as the operating speed of the driver is stabilized and reaches a predetermined value, the primary electrical generator is then being driven and activated thereby. By the aforesaid hybrid power-generating device, not only the overall performance and the stability of power grid are enhanced, but also the operating cost is reduced.