In this study, to solve the problem of excessive NO x emission of W-shaped radiant tube (WRT) burning coke oven gas (COG), the numerical calculation method was adopted to investigate the effects of N 2 and CO 2 as diluent gases in the air, CH 4 as a diluent gas in the fuel, and blast furnace gas as a diluent gas for COG on NO x emissions of WRT. Besides, a novel WRT (N-WRT) with a flue gas circulation structure was developed to reduce NO x emissions. Moreover, the effects of the nozzle diameter and nozzle location on the gas flow, temperature distribution, and NO x emission were analyzed and discussed in detail. The results shows that CO 2 as a diluent can inhibit the production of NO x more than N 2 . The high NO x emission of the COG-fired WRT is caused by a higher proportion of H 2 and CO in COG. The NO x production of the WRT is about 6 times that of the N-WRT, indicating the effect of circulating flue gas on reducing NO x emission is quite remarkable.