In order to investigate the durability damage characteristics and degradation law of highland barley straw ash modified magnesium oxychloride cement mortar protected concrete, reinforced concrete specimens with different thicknesses of protective layers were prepared. The corrosion degradation of steel bars was tested and analyzed by constant current accelerated corrosion test under salt brine erosion environment. The cracking situation of concrete during the erosion process was monitored by concrete crack defect detection instrument, and the electrochemical parameters obtained based on AC impedance analysis and polarization curve fitting were used to characterize the corrosion degradation of internal steel bars. A numerical model of durability damage degradation of magnesium oxychloride cement mortar protected concrete was established using Weibull distribution function. The results show that under salt brine erosion environment, the corrosion current density of steel bars in magnesium oxychloride cement mortar protected concrete with highland barley straw ash added is still less than 0.2 μA·cm-2 after 648 h of current passing, indicating a low corrosion state and a slow corrosion development. The Weibull distribution function can effectively predict the degree of corrosion degradation of steel bars in highland barley straw ash modified magnesium oxychloride cement mortar protected concrete.