The utility model discloses a steel inclined strut used for a water pier super-long prestress bent cap construction supporting system. The steel inclined strut is provided with two opposite jack stays equal in length and parallel to each other, the two jack stays are connected together through a steel structure, a pin hinge and a supporting base thereof are connected to the bottom end of each jack stay, the pin hinge supporting bases are connected with a water pier bearing platform through pre-embedded steel plates, the bottom ends of the jack stays are connected with the pin hinge supporting bases through the pin hinges, an annular groove is formed in the tail of each pin hinge, an axial limiting baffle is inserted into each annular groove and fixed to the corresponding pin hinge supporting base, and a horizontal supporting cover plate is arranged at the top end of each jack stay. The steel inclined strut is high in rigidity and bearing capacity, capable of shortening the construction period, reducing labor cost and material cost, recyclable, and suitable for the water pier super-long prestress bent cap construction supporting system, wherein the length of the construction supporting system is larger than 40 m, the installing height of the construction supporting system is larger than 8 m, and the clear distance between pier bodies is larger than 18 m.