The weather resistance of 10CuPRE、10CuP and Q235 steels were studied by dry-wet cyclic immersion test. The corrosion resistance mechanism of rare earth Cu-containing weathering steel was studied through electrochemical polarization test, scanning electron microscope(SEM) and X ray diffraction(XRD). The results show the small and spherical rare earth oxysulfides replace the elongated MnS inclusions in the rare earth weathering steel. Less and fewer rare earth oxysulfides heavily decrease pitting susceptibility and rate of pit propagation. So the electrochemical corrosion of microarea in the steel matrix is weakened after rare earth was added in the Cu-containing weathering steel. The inner rust layer of rare earth weathering steel is more compact and uniform than that of weathering steel without rare earth. The main corrosion product on the rare earth weathering steel is α-FeOOH. The formation of the steady corrosion product is promoted by rare earth, which result in that the protective property of the inner rust layer on weathering steels is enhanced. As a result, the corrosion resistance of Cu-containing weathering steel is improved by rare earth elements.