The work aims to improve the corrosion resistance of A572 Gr.65 steel. A572 Gr.65 steel with different RE contents was obtained by adding mixture rare earths with La and Ce. The electrochemical corrosion behavior of A572 Gr.65 steel with different rare earth contents was analyzed by electrochemical workstation, XRD and SEM with 3.5%NaCl solution corrosion medium. The rare earth made the corrosion potential shift positively and decreased the corrosion current. When the rare earth content was 0.0047%, the corrosion potential was the most positive of -0.50 V and the corrosion current was the minimum of 2.77×10-6 A/cm2. The anode part of the polarization curve had obvious transition zone of activation-passivation and passivation process. The impedance spectroscopies of A572 Gr.65 steel with different RE contents were composed of single capacitive reactance arc. The radius of the capacitive reactance arc represented the ability to hinder the transfer of charge. When the rare earth content was 0.0047%, the radius of the capacitive reactance arc was the largest and had maximum ability to hinder the transfer of charge. The rare earth could change the property of the inclusions in the steel. RE transformed inclusions from CaS and Al2O3-CaO to RE2O2S and the size of inclusions changed from 5 μm to 2 μm, so the active area of corrosion decreased. The rare earth ions improved the polarization rate of cathode and made the content of unstable γ-FeOOH decrease, so the stability, density and adhesive ability of the rust layer increased. The charge transfer resistance was raised, thus effectively preventing the invasion of the corrosive Cl–. The rare earth can effectively improve the corrosion resistance of A572 Gr.65 steel. When the rare earth content is 0.0047%, the experiment steel has the best corrosion resistance. In the process of corrosion, corrosion changes from pitting corrosion to uniform corrosion, so the formation of active point and the rate of anodic dissolution are the restrictive links.