Dualphase steel 09CuPCrNi was prepared through intercritical quenching process. The influence of dualphase treatment on corrosion resistant property of the steel was studied by electrochemical potentiodynamic test and salt spray test. The results indicate that the corrosion behavior of the dualphase weathering steel quenched at 780 ℃ and original weathering steel in 5%NaOH, 5%HCl, 5%H2SO4 and 3.5% NaCl aqueous solutions was identical, but the dualphase steel showed lower corrosion current. In salt spray test, the corrosion rates (mm/a) of dualphase steels were lower by 7.9%~22.2% (48 h) and 2.3%~130% (120 h).