The deep control of the coal combustion process is the ultimate goal pursued by coal combustion researchers. Based on the gas conversion and the solid functional group conversion,the C/O/N element migration discipline of the fuel in the four reducing atmosphere regions was mainly analyzed and elaborated during the pulverized coal preheating combustion process. From the gas transformation analysis,it can be obtained that the carbon element in the whole process is mainly released in the form of CO and CO2,the oxygen element is mainly released with gaseous carbon oxide and nitrogen oxide,and the nitrogen element is mainly released in the form of N2 during the preheating stage. It is mainly released in the form of NO2 and NO during combustion stage,its nitrogen-containing form is related to the distance from the top of the combustion chamber. From the analysis of solid functional group transformation,it can be seen that the types of carbon-containing double bonds and nitrogen-containing functional groups on the surface of raw coal increase after preheating. In the three reducing regions of the combustion chamber,the carbon-containing double bonds on the fuel surface are consumed and generated for many times,the adsorbed oxygen on the surface is released and adsorbed for many times,and the types of nitrogen-containing functional groups also change. The preheated char and the solid sample at 400 mm generate the most carbon-containing double bonds and there is the regeneration of adsorbed oxygen,thus the samples generated at these two positions are the most active. The samples at 100 mm and 900 mm contain the most types of unstable N-containing functional groups,which makes the nitrogen in the sample easier to be released in the form of gas at these two locations. The experimental results can provide basic experimental data support for the depth control of NOx during coal combustion.