The long-term corrosion resistances for the carbon steels have been investigated under high temperature pressurized water atmosphere, in the conjunction with the analysis of nondestructive properties by the ultrasonic wave. The corrosion test for carbon steels was carried out at the temperature of 200 °C under a water pressure of 10 MPa. The corrosion test cycles for carbon steels were changed up to 65 weeks. The mechanical properties of carbon steel suffered from the corrosion cycle were investigated by a tensile test, attaching an acoustic emission sensor on the test sample. The tensile strength of carbon steels greatly decreased beyond the corrosion cycle of 35 weeks, accompanying the increase of weight loss by the creation of corrosion damages. The attenuation coefficient of carbon steels by the ultrasonic wave increased with the increase of corrosion cycles.