Abstract: The self-passivating behavior of 316L stainless steel in acetic acid solution was studied. The constant current polarization curve and the corrosion potential-to-time curve were measured. The results showed that passivation film was formed by three layers:oxides of Fe and small amount Cr in the first layer; oxides of Cr and small amount Fe, Mo, Ni in the second layer; and oxides of Mo, Ni and small amount Fe in the third layer. The structure model of passivation film can explain the electrochemical results well.