Abstract: To suppress the fluctuation of the renewable energy in microgrid, the authors took a microgrid composed of photovoltaic generation, diesel generation, battery and supercapacitor as an example and analyzed the action of supercapacitor to suppress power fluctuation in microgrid by the frequency domain method. Based on the given distributed generations and their control system model, the supercapacitor effects in grid-connected microgrid were analyzed from the aspects of the most controllable fluctuation frequency, the largest access capacity of PV and the suppression effect in the whole frequency band of the frequency spectrum. The simulation and practical experiment results demonstrate that the supercapacitor can raise the controllable disturbance frequency in the microgrid, increase the PV penetration and suppress the fluctuation within the whole scale of frequency.