The efficient use of coal resources and the safe operation of coal-fired boilers are hindered by high-temperature corrosion caused by corrosive sulphur components. To predict the impact of sulphur−nitrogen interactions on sulphur’s evolution and its mechanism of action, a conventional sulphur component evolution model (uS−N) and an improved sulphur component evolution model (S−N) that considers sulphur−nitrogen interactions were proposed in the present study. The models were built using OpenFOAM−v8 software for the coal combustion process, and the generation of SO2, H2S, COS, and CS2 was simulated and analysed under different air excess coefficients. The simulations were conducted to analyse the patterns of SO2, H2S, COS, and CS2 generation at different air excess factors. The results show that, compared with the uS−N condition, the simulated values of coal combustion products (SO2, H2S, COS, and CS2) under the S−N condition were closer to the experimental values, and the errors of different sulphur components at the furnace exit were all less than 5%. As such, the S−N model can more accurately predict the evolution of sulphur components. In the simulation range, when the air excess factor increased from 0.7 to 0.9, the production rate of SO2 increased, while the production rates of corrosive sulphur components H2S, COS, and CS2 decreased significantly by 41.3%, 34.8%, and 53.8%, respectively. Further, the mechanism of the effect of sulphur−nitrogen interactions on the generation rates of different components was revealed at different air excess coefficients. Here, the effect of sulphur−nitrogen interactions on SO2 and COS was found to be more significant at smaller air excess coefficients, and the effect of sulphur−nitrogen interactions on H2S and CS2 was more significant at larger air excess coefficients. The present study can provide a theoretical basis for predicting the evolution of sulphur components during coal combustion and improving the high-temperature corrosion problems caused by such a process.