The invention discloses a secondary vertical rotating construction method for an arch rib of a long-span steel arch bridge, which comprises the following steps of: dividing an arch rib into an upper section and a lower section; finishing assembly on an arch rib bracket and articulating the upper section and the lower section of the arch rib by a middle hinge; articulating the bottom end of the lower section of the arch rib and a bottom hinge; vertically rotating the arch rib to the position twice in such a way that an anchoring system is provided with a traction rope, an upper fastening rope and a lower fastening rope; and finally installing a closure section. The invention fully utilizes terrains at both sides of a V-shaped valley, reduces the bracket engineering amount, converts high-altitude operation into assembly and welding of the arch rib on a bracket which is closer to the ground, effectively reduces construction risk and greatly improves construction quality.