Anaerobic bacteria, especially sulfate-reducing bacteria (SRB), play an important role in the corrosion of steel in marine environment. Considering the marine immersion corrosion of mild steel, the present paper presented environmental scanning electron microscopy(ESEM) morphology images and energy dispersive spectroscopy(EDS) elemental analysis to illustrate the formation process of corrosion product layer on the steel surface induced by the metabolism activity of SRB. The results showed that in the accelerated conditions three layers of corrosion product with different composition and configuration were formed step by step on the steel surface. The metamorphosis of the iron in the steel to forms of iron oxide and to iron-sulphur compounds was also involved.