The invention relates to a system, a device and a method for preparing active carbon, which improve the recovery rate of the active carbon. The invention adopts the technical scheme that the system comprises a pyrolysis treatment subsystem for carrying out pyrolysis treatment on pretreated materials and an active carbon finishing system for further sorting and dewatering a primary active carbon product; in the system, a carbonization and activation integrated furnace of microwave heating and hermetic low-temperature pyrolysis processes is used as main equipment of the pyrolysis treatment subsystem; materials are cracked in a pyrolysis furnace chamber, and carbonized solid residues after cracking enter an activation chamber and processed into a primary active carbon product; and then the primary active carbon product is turned into an active carbon finishing subsystem, a carbonization and activation integrated furnace atmosphere guaranteeing system matched with the pyrolysis treatment subsystem and a gaseous product recycling system. The invention sufficiently utilizes products and energy in the process of production and has compact operation process and strong reliability.