In this present work, non-equilibrium coatings (like glassy state but not amorphous texture) were prepared by electric arc spraying using Zn-Al-Mg-RE-Si powder core spun alloy, and the effect of Mg content on corrosion resistance of coatings and the electrochemical properties of alloy coatings in corrosion process were investigated by CASS test, weight-loss test, XRD, SEM, polarization curves and electrochemical impedance spectroscopy. The results indicate that: The corrosion process of non-equilibrium coatings in CASS test includes corrosion inhibition stage and substrate corrosion stage; There appears much micro-crystallite and exists grain refinement in corrosion process; Before CASS test, the corrosion potential of non-equilibrium coatings shuffles when Mg content increases; Before CASS test and after CASS test at 120h and 216h, the corrosion current density approaches the minimum value and the corrosion rate is slowest when Mg content is 2%. Before CASS test, there appears the feature of Warburg impedance, but there did not appear the feature of Warburg impedance after CASS test at 120h and 216h. When Mg content is 2%, the charge-transfer resistance of coating is obviously higher than the coatings with other Mg content. Finally, an optimization composition of non-equilibrium coating—Zn-Al-2Mg-RE-Si coating is obtained by synthesis comparing.