The invention provides a method and device for restraining power fluctuation of a wind generation set based on flywheel energy storage. A flywheel energy storage device is connected to a power output point of the wind generation set, the flywheel angular speed of a flywheel energy storage system is adjusted, the power of the outlet of the wind generation set is adjusted through the momentum increment of the flywheel energy storage device, then, peak eliminating and valley filling and power smoothing are conducted, and the voltage of the outlet is stabilized.