To investigate the effects of hydrogen sulfide (H₂S) on the combustion characteristics of methane (CH₄) in atmospheric pressure range, the 0-D and PFR reactors were adopted in CHEMKIN-PRO chemical kinetics software to investigate the effects of H₂S concentration, excess air coefficient, pressure and temperature on CH₄ ignition delay and NO reduction, meanwhile sensitivity analysis was used to reveal the chemical kinetics mechanism. The modeling results showed that the H₂S could promote the formation rate of active groups (H, O, OH, HO₂, HO₂, H₂O₂), so premixed gas ignition delay time was reduced, and the effect was more obvious at low temperature. The premixed gas ignition delay time is decreased with the increase of excess air coefficient and pressure. The H₂S decreases the CH₄ reaction temperature and reductive group CH_i are generated at lower temperature, so the H₂S decreases the temperature of NO reduction by CH₄/H₂S. But the existing of H₂S reduces NO reduction efficiency to a certain extent, and the effect is more remarkable in fuel-rich atmosphere.