These days, most of the marine structures which are constructed and used in Persian Gulf, are made of ST37 steel. Due to oil and gas sources excavated, the number of these structures is constantly increasing. On the other hand, these types of structures are exposed to corrosive environments and it is seriously critical for these structures to be used for many years. Coal tar epoxy (trade name), one of the popular coating layers, is used in different parts of steel constructions which are in use in the Persian Gulf. Several works have been carried out on the functioning quality of this coating in tidal zones, under splashing water and atmospheric conditions, but up to now no report is made in submerge zone. Hence in this investigation, three coating systems have been considered that coal tar epoxy is being used in each of one of the three layers of primer, middle and top. Two systems of laboratory and in field have been investigated for 6 months and an isolated system in field type has been also investigated. All the mechanical and chemical tests which have been performed are according to NACERPO176-64 standard which is for investigating the function of all marine coatings. All corrosion tests have been performed in Refinary Laboratory of Petroleum Industry and all the fields samples have been investigated in Steel Harbor located in the south of Bandar Abbas every week during 6 months. The test results have indicated that the coal tar epoxy which were being used in the last layer is not suitable for submerge zone. By preparing, however, a suitable surface in the first layer using zinc ethyl silicate and the last layer with antifouling, the coal tar epoxy can function properly in the middle layer.