The present invention discloses one process of adding oxygen to carbon activating reaction tail gas for circular utilization in active carbon preparation. The mixture of CO2 and water vapor and carbide are made to produce activation reaction at high temperature circumstance to prepare active carbon, the reaction produced CO is collected and burnt with added oxygen to form activating CO2 gas, and the formed activating CO2 is made to react with carbide material to prepare active carbon. The apparatus for the circular utilization process includes activating furnace with CO exhaust port, heating furnace around the activating furnace, and combustion reactor in the CO exhaust port. The present invention has the advantages of utilizing tail gas to lower production cost, etc.