Abstract: The combustion experiment of an existing double P type radiant tube and the corresponding CFD simulation were performed in this paper. By contrast, the maximum error of NO_x concentration between numerical calculation and experimental data is 3.6%, and the deviation of the other parameters is less than 1%. Then the concept of air classification was applied to the double P type radiation tube to design a belt pipe nozzle hierarchical gas-fired radiant tube. The flow and heat transfer characteristics were studied. The results show that when air into the branch pipe accounts for 25% of the total amount of air, the radiant tube wall temperature and thermal efficiency are the highest. When the content of gas into the branch is 20%, the radiation tube wall temperature realizes the minimization and the uniformity of wall temperature is the best. When both air and gas at the same air-fuel ratio are introduced into the branch pipe, and the volume of air and fuel gas is 25% of the total amount of gas, the gas temperature distribution in the radiant tube is the most uniform. When the volume of air and fuel gas into the branch pipe increases from 5% to 35%, the wall surface temperature decreases first and then increases slowly; when it is 20%, the radiation tube wall temperature reaches a minimum.