The work aims to study the effect of corrosion time on the corrosion behavior of Q345 steel in a 4 g/L S2O32? based solution of sodium aluminate, to explore the law of corrosion and to clarify the corrosion mechanism. Salt corrosion and electrochemical corrosion methods were used to explore the corrosion behavior of Q345 steel by corrosion weight loss, polariza-tion curves, impedance spectroscopy, SEM and EDS. When the corrosion time was extended from 3 d to 7 d, the corrosion weight loss increased from 2.4505 g/m2 to 2.6420 g/m2 and the pitting depth increased from 3.3 μm to 4.6 μm. After 7 d, the corrosion weight loss and pitting depth tended to be stable. Corrosion rate equation was V=2.426t?0.975 and corrosion rate drastically decreased from 1 to 3 d. Initial corrosion current density was relatively large and corrosion current density rapidly decreased from 6.538 μA/cm2 to 0.785 μA/cm2 from 3 d to 5 d and then gradually decreased to 0.308 μA/cm2 on 9 d. Both the radius of capacitive reactance and the charge transfer resistance Rct increased with the increase of corrosion time. If the corrosion time prolonged, the content of O, Al, S and other elements in the product increased, and the content of Fe decreased. At the initial stage of corrosion, OH? preferentially is adsorbed to form denser Fe3O4 and FeOOH. At the middle stage of corrosion, S2O32? reacted with the matrix to form FeS with weaker adhesion. Thus, the structure of Fe3O4 becomes unstable and falls off and the structure of the product is loose. At the late stage of corrosion, Al(OH)3 is transformed into Al2O3, and AlO2? and Fe3O4 to form spinel FeAl2O4. The denser structure covers the surface of the substrate, hinders the contact between the corrosive medium and the substrate and reduces the corrosion rate.