Pulverized coal-fired boilers applying low-NOx combustion technologies usually produced high-concentration H2S, which is one of the main reasons for high temperature corrosion. Accurate prediction of sulfur species, especially H2S, is of great significance for the design and operation of pulverized coal-fired boilers. According to the previous research results, an accurate detailed reaction mechanism of gaseous sulfur species was presented and it’s prediction results were consistent with the previous experimental data. After the rate-of-production analysis, the key elemental reactions affecting the formation or consumption of gaseous sulfur species were determined, which can provide some help for the prevention of high-temperature corrosion.