Abstract: The program Chemkin was used to investigate effect mechanism of existence patterns of sulfur on reduction of NO under poor oxygen condition. Three factors such as combustion of hydrocarbon, formation of NOx and interaction between sulfur and nitrogen were considered. The results show that reaction of HCN oxidation to NO finishes in milliseconds, whereas the reduction process of NO is gentle, finishing in seconds. SH and SN are important matters for direct reduction of NO under poor oxygen conditions. The reaction between SH and NO is intense, because concentration of SH increases after addition of SO2. As a result concentration of NO decreases. Therefore, existence patterns of sulfur can promote reduction of NO effectively under poor oxygen condition.