To understand the effect of CO2 on fuel N evolution during rapid coal pyrolysis, pyrolysis/gasification of EH lignite and HL bituminous coal were carried out in a suspension-bed reactor under N-2 or CO2 atmosphere. The chemical and physical structures of the chars were measured by Fourier transform infrared spectrometry and X-ray diffractometry. The results show that higher temperature is favorable for the evolution of HCN and NH3. Thermally stable quaternary N is believed to be the important intermediate for the formation of NH3. The presence of CO2 can promote HCN and NH3 generation through the creation of H radicals and the cracking of N-containing groups. However, the HCN yields of HL coal pyrolyzed in CO2 at 700 and 800 degrees C are lower than that in N-2, and a similar result was obtained for EH coal at 1000 degrees C, which are caused by the blocking effect of CO2 and the reaction of HCN with CO2, respectively. Structural analyses of the chars show that in the initial stage of coal pyrolysis/gasification, CO2 can suppress the polymerization of aliphatic chains and more H is retained as -CH2 or -CH3 in chars. Subsequently, gasification of CO2 with the rich aliphatic chains is helpful to produce abundant H radicals for the formation of NH3.