The utility model discloses an inverted-cone-shaped steel jacket box in construction of a precast tie beam of an underwater pier foundation, which is characterized in that the steel jacket box is formed by connecting sections section by section, the bottom section is inverted-cone-shaped, and the diameter of a bottom cone opening is slightly larger than that of a pile foundation steel casing, so that the bottom section can be sleeved outside the pile foundation steel casing; a concave notch is formed in the top of the bottom section and used for containing the prefabricated tie beam; the adjacent sections are connected through flanges; in the construction process, the bottom section of the steel jacket box, the prefabricated tie beam and the first section of the steel jacket box are spliced, and the whole set of box tie beam is combined; sinking the whole sleeve box tie beam along the pile foundation, and connecting the upper sections of sleeve bodies on the water surface section by section to form lengthened sections; and bottom sealing underwater concrete is poured into a gap between the steel jacket box and the pile foundation, and a water-free space is formed in the steel jacket box for water-free operation. The construction is simple, the cost is low, the safety is good, and the work efficiency can be improved.