Abstract: The formation of sulfide in oil tank is simulated. The reaction of hydrogen sulfide with iron oxide black of different temperature and different relative humidity under the conditions of oxygen free, and the oxidation tendency of formed sulfide are studied. The result shows that the relative humidity of the sample plays an important role in oxidation tendency of sulfide. The strongest oxidation tendency of sulfide formed at relative humidity of 5%-20% at room temperature and at relative humidity of 10%-20% above 50℃, which will result in the most serious threat to the safe running of oil tanks. The oxidation tendency of sulfide formed at relative humidity of 0% or above 20% is weak, and there is no risk to the safe running of oil tanks.