The invention discloses a water-blocking composite cable for an offshore oil platform. A cable core comprises a skeleton, wherein the skeleton comprises two partially overlapping square skeletons; theskeletons of an overlapping part are primary skeletons; the skeletons of non-overlapping parts are secondary skeletons; the primary skeletons and the secondary skeletons are of an integral structure;a power line core is arranged in the primary skeletons; a control line core and a communication line core are arranged in each secondary skeleton separately; and the outer side of the cable core is sequentially coated with a cross-linked polyethylene inner sheath, a steel-tape braided armor layer and a cross-linked polyethylene outer sheath from inside to outside. The water-blocking composite cable is provided with the skeleton; the skeleton comprises two partially overlapping square skeletons; the skeletons of the overlapping part are the primary skeletons; and the skeletons of the non-overlapping parts are the secondary skeletons, so that the water-blocking composite cable plays a good protecting role in the power line core, the control line cores and the communication line cores separately, and meanwhile, the compression and tension resistance of the cable can be strengthened.