Abstract: In order to solve the problem of deterioration of mechanical properties of reinforced concrete (RC) beam in coastal zoneunder normal working condition of the larger load, the mechanical behavior deterioration of RC beam specimens was investigated by static loading test, after they experienced 180 d atmospheric environment and 180 d seawater spraying dry-wet cycle (Simplified by Ⅰ corrosion); or they experienced 180 d seawater spraying dry-wet cycles and180d atmospheric environment (Simplified by Ⅱ corrosion) by the laboratory simulation. Test results yielded load P_y, limited load P_m, and ductility factor u of them decreased when the beam specimens were acted on by sustained damage load in Ⅰ corrosion (or Ⅱ corrosion); and P_y P_m and u decreased more with the sustained damage load increasing; the decrease of P_y P_m and u for the beam specimens in Ⅱ corrosion were greater than those of P_y P_m and u for the beam specimens in Ⅰ corrosion. The flexural stiffness of the beam specimens became smaller with the increase of the sustained damage load. The experimental results show that the effect on the mechanical properties of RC beams is obvious form the larger sustained damage load and certain corrosive environment.