The nitrogen transformation during the oxy-fuel combustion of coal and biomass mixtures was studied through thermogravimetrymass spectrometry (TGMS). Influence factors, such as atmosphere and biomass share, were selected to study the release of four nitrogenous gases HCN, HNCO, NH3, and NO. With the presence of >= 20% O-2, the combustion of Datong coal and biomass mixtures releases less HCN, NH3, and NO and more HNCO in the O-2/CO2 atmosphere compared to the O-2/N-2 atmosphere. HCN and HNCO compete mutually during the formation of nitrogenous gases. The mixtures of Datong coal and biomass release more nitrogenous gases than Datong coal alone in both O-2/CO2 and O-2/N-2 atmospheres during the devolatilization. With the O-2 concentration in the O-2/CO2 atmosphere increasing from 20 to 100%, the relative yields of NH3, HCN, and HNCO produced from the mixtures decrease, while the NO yield increases. The HNCO yield changes greatly with the increase of the O-2 concentration because of the oxidation by OH. Increasing the biomass share in the mixtures improves the relative yields of nitrogenous gases. The biomass share can greatly affect the HCN and HNCO yields, owing to the different forms of N-containing structures between coal and biomass.