Abstract: The electrochemical testing of Q235 steel was carried out by AC impedance and potentiodynamic polarization curve technique, and the surface corrosion morphology was observed by metallographic microscope. The effects of different ₂S/CO₂ ratios on the electrochemical corrosion behavior of Q235 steel in ₂S-CO₂ system were studied and the corrosion mechanism was investigated. The results show that in ₂S-CO₂ system, CO₂ has a certain degree of inhibition on the corrosion of ₂S. ₂S accelerates the corrosion of CO₂ on Q235 steel. When ₂S/CO₂ is 2:1, the corrosion rate of Q235 steel is largest.