<p>The purpose of this study is to clarify the corrosion process of the rust layer formed on weathering steel (WS) and to identify its electrochemical properties. At the initial stage, different SO₄^2- concentrations cause the anode and cathode current densities to propagate unevenly; the imbalance in current densities promotes the corrosion reaction. With the corrosion process prolonging, under the low SO₄^2- concentration, the continuous acid regeneration reaction accelerates the corrosion process, leading to a higher corrosion rate. Under the higher SO₄^2- concentration, SO₄^2- promotes the conversion of γ–FeOOH to α–FeOOH. This mechanism raises the quantity of α–FeOOH and makes the electrode potential shift positively. As a result, the electrochemical process is hindered, causing a reduction in the corrosion rate. At the low SO₄^2- concentration, the growth of a protective oxide layer is blocked. At the higher SO₄^2- concentration, the rust layer exhibits self-healing properties, which are helpful in forming a protective rust layer.</p>