The invention discloses a two-step activation preparation method of activated carbon and application thereof in a supercapacitor. The method comprises the following steps that blind coal is smashed and sieved, and an additive and a binder are added to be stirred; the mixture is added into a muffle furnace to be carbonized and then, shifted into a tubular activating oven, activated gas is introduced to be activated; diluted hydrochloric acid is used for acid pickling, filtering is performed, then, distilled water is used for washing, and a KOH solution is used for dipping; one-time activated carbon is placed into the activating oven, and protective gas is introduced to be activated; diluted hydrochloric acid is used for acid pickling, filtering is performed, then, distilled water is used for washing till pH is 7, and then drying is performed; reactivated de-ashing activated carbon is uniformly mixed with ethylene and polytetrafluoroethylene after being ground, the mixture coats foamed nickel, and after drying is performed, tabletting is performed to prepare the supercapacitor. Blind coal is adopted as a raw material, reaction conditions are mild, on the basis of the conventional activated carbon production technology, reactivation and de-ashing are performed, the synthesis cost is greatly lowered, and the huge application and popularization potential is achieved in the field of activated carbon for the high-performance supercapacitor.