The invention relates to a heating treatment device used for an Austenitic grain size carburization test and a using method thereof. The method comprises the following steps that (1) a carburizing catalyst is paved at the bottom of a tank body, activated carbon is paved above the carburizing catalyst and located below an air permeable partition plate, a plurality of samples are placed on the air permeable partition plate in a non-contact mode, and the top end of the tank body is covered with a sealing cover for sealing; and (2) the heating treatment device is placed into a box type resistance furnace, in a high-temperature state, CO2 decomposed by the carburizing catalyst reacts with the activated carbon, thus CO is compounded, a stable carbon potential atmosphere is formed on the peripheries of the samples through the air permeable partition plate, an atmosphere carburizing mode is simulated to form a carburizing layer, and the carburization test of the Austenitic grain size of the samples is completed. According to the heating treatment device used for the Austenitic grain size carburization test and the using method thereof, the carburization test of the Austenitic grain size can be achieved in the regular box type resistance furnace, test cost can be reduced, and test efficiency is improved; and the carburizing heating treatment quality is good, the carburizing layer is uniform, and the examination requirement of the carburization Austenitic grain size is met.