From September 1992 to September 1995, the corrosion behavior of three marine steels was studied in Chengdao offshore area by means of individually and electro-connectedly hanging plates to obtain data for anticorrosion design of oil-exploitation structures there. The variation trend of corrosion rate with exposure time showed that the variation curves and degrees of the three steels’ corrosion were generally identical and had nothing to do with the exposure time. The whole change trend of corrosion rates in three years showed that the corrosion rates of 20~ # steel were nearly identical in different positions, each of which was a little lower than that of 16Mn steel specimens in corresponding positions, and also was lower than that of Q235A steel specimens in tidal zone and immersion zone. Although 20~ # steel corroded rapidly at first, its corrosion rate had decreasing trend during long-term service. Therefore, 20~ # steel is feasible to be applied for a long time in various marine zones, especially nearby the low tidal line and immersion zone. The results of Q235A steel, 16Mn steel and 20~ # steel by means of electrically connected hanging plate in three years indicated that the corrosion of the steel specimens in splash zone was the most severe as a result of the dry-wet cycle and macrocell effect. Specimens in the other positions corroded mildly, and that in tidal zone corroded most slowly. The corrosion rate of 20~ # steel was the highest among the three steels in the test, and the corrosion rates of Q235A steel and 16Mn steel were identical on the whole. When the specimens were hanged electro-connectedly, the macrocell effect generally tended to increase with exposure time. The highest corrosion rate of Q235A_ steel in the splash zone in the three years was about 0.278 mm/a, while that of 16Mn steel was about 0.321 mm/a, and that of 20~ # steel was 0.330 mm/a or so. In contrast, the corrosion rate of the steels in the tidal zone was the lowest in three years, and were 0.052 mm/a(Q235A steel), 0.048 mm/a(16Mn steel )and 0.040 mm/a(20~ # steel). From September 1992 to September 1995, the corrosion behavior of three marine steels was studied in Chengdao offshore area by means of individually and electro-connectedly hanging plates to obtain data for anticorrosion design of oil-mining structures there. The variation trend of corrosion rate with exposure time showed that the variation curves and degrees of the three steels’ corrosion were generally identical and had nothing to do with the exposure time. The whole change trend of corrosion rates in three years showed that the corrosion rates of 20 ~ # steel were nearly identical in different positions, each of which was a little lower than than of of 16Mn steel specimens in corresponding, also was lower than that of Q235A steel specimens in tidal zone and immersion zone. corrosion rate had decreasing trend during long-term service. Therefore, 20 ~ # steel is feasible to be applied for a long time in various marine z ones, especially nearby the low tidal line and immersion zone. The results of Q235A steel, 16Mn steel and 20 ~ # steel by means of electrically connected hanging plate in three years indicated that the corrosion of the steel specimens in splash zone was the most severe as a result of the dry-wet cycle and macrocell effect. Specimens in the other positions corroded mildly, and that in tidal zone corroded most slowly. The corrosion rate of 20 ~ # steel was the highest among the three steels in the test, and the corrosion rates of Q235A steel and 16Mn steel were identical on the whole. When the specimens were hanged electro-connectedly, the macrocell effect generally tended to increase with exposure time. The highest corrosion rate of Q235A_ steel in the splash zone in the three years was about 0.278 mm / a, while that of 16Mn steel was about 0.321 mm / a, and that of 20- # steel was 0.330 mm / a or so. In contrast, the corrosion rate of the steels in the tidal zone was the lowest in three years,and were 0.052 mm / a for Q235A steel, 0.048 mm / a for 16 Mn steel and 0.040 mm / a for 20 ~ # steel.