The spontaneous combustion of iron sulfides in sour oil tanks is thought to be the main reason to cause fire and explosion accidents in oil tanks. Sulfur hydrogen dissolving in water to form hydro-sulfuric acid reacts with iron to give iron sulfides. The gas of sulfur hydrogen was continuously passed through the water, at a flow rate of 300 mL/min for 6 h, in trigonal beaker contained 8 g iron powder to produce the iron sulfide samples at 25, 50 and 75 ℃ respectively. The deposit was filtered and dried. The reaction product was analyzed by chemical and XRD analysis. The results show the iron sulfide in reaction product is FeS. Air passed through the dry and moist reaction product at a flow rate of 300 mL/min respectively. The experimental results show that all the reaction products are of high spontaneous combustion nature. When sulfuration temperature is increased, the sulfuration reaction rate rose and the spontaneous combustion nature of reaction product are also raised.