The corrosion was accelerated and tested by immersion in magnesium chloride solution, electrochemical test of coated steel bars in magnesium oxychloride cement concrete was carried out, and the characterization of corrosion current density for the corrosion of the coated steel bars was studied. Taking corrosion current density as the degradation index the least squares method, the moment estimation method and the maximum likelihood method were used to estimate the parameters, the corrosion prediction model of the coated steel bar was established based on the Weibull function. And then scanning electron microscopy and X ray diffractometer were used to conduct microanalysis on the coated steel bar to judge the protective effect of the coating. The results show that the Weibull function can well reflect the degradation process of the coated steel bar, and the least squares method can well describe the durability degradation process of the coated steel bars. The failure time of coated steel bar is about 38000d(104.1 a), the failure time of R(t0.4) is 2960d(81a). The coating can protect steel bar in concrete from corrosion.