Hot dip galvanized-, cold galvanized- and Zn-rich coating coated-plain carbon steels were exposure in the seawater of Zhong-gang harbor at Qingdao for five years. Then the long-term immersed steels were characterized by means of EDS, XRD and FT-IR, especially in terms of the interface of seawater/steel. It follows that for the steel plate with Zn-rich coating, cracks emerged at edges and conners, and occurrence of coating falling off on the surface could be observed, which indicates that the coating has generally failed; Meanwhile, both the cold-dip galvanized and hot-dip galvanized plates maintain good barrier performance, and the elemental X-ray mapping reveals that there exist Zn of homogeneous distribution on their corroded surface, to which the better protectiveness of the two Zn galvanizing coatings may be ascribed. Among others, the hot-dip galvanizing is the best in corrosion resistance. The results of characterization for fouling organism on the surface of steel plates show that there is no significant difference in the fouling process in the formation of micro biofilm or the large fouling biological community among the three materials. Comprehensive comparison of corrosion and fouling of steel plates show that the corrosion protectiveness of the three coatings may be ranked in the order as follows: hot dip galvanizing＞cold galvanizing＞zinc rich coating.