The invention relates to a marine three-dimensional oil tank platform, system and a constructing method of the marine three-dimensional oil tank platform. The marine three-dimensional oil tank platform comprises at least three pile columns or at least three buoyance cylinders connected to the bottom of the sea, an underwater oil tank connected between all the pile columns or all the buoyance cylinders and a supporting frame arranged at the top of all the pile columns or all the buoyance cylinders, wherein an aquatic oil tank is arranged on the supporting frame; a plurality of gravity anchors anchored to a seabed or a sea bottom are connected to the underwater oil tank; the underwater oil tank is located below a sea level, and the aquatic oil tank is located above the sea level; a cavity ofthe underwater oil tank mutually communicates with a cavity of the aquatic oil tank; the system comprises a plurality of seawater three-dimensional oil tank platforms which are in parallel connection; and the pile columns or the buoyance cylinders can adopt the buoyance cylinders and a sea bottom fixing system of the buoyance cylinders or the pier columns and a sea bottom fixing system of the pier columns. The marine three-dimensional oil tank platform disclosed by the invention is simple in structure and optimized in design, after the marine three-dimensional oil tank platform floats to an offshore region, only a small quantity of working capacity of assembling and reinforcing is needed, so that the constructing difficulty of an offshore platform and the investment of offshore transporting and assembling equipment are reduced, and the construction cycle is shortened; and the constructing method is easy to construct, high in reliability, and suitable for oil gas exploitation work in the marine field.