The invention discloses a method for preparing active carbon by potassium alkoxide as an activating agent. According to the method, wood or bamboo raw materials take the potassium alkoxide as the activating agent. The active carbon prepared by the method is less in use amount of the activating agent, is environment-friendly and is simple in equipment requirements; the specific surface area of the prepared active carbon is 1860-2300m<2>/g; the iodine sorption value is 1150-1535mg/g. According to the active carbon prepared by the method, the problems that strong acids (H2SO4 and H3PO4), strong alkalis (KOH and NaOH), ZnCl2 and the like are used as the activating agent in the process of preparing the active carbon by using a traditional chemical method, the corrosion to equipment is serious, the pollution to the environment is great and the like are solved. The technology successfully has obvious economic and social benefits.