The invention belongs to the technical field of bridge maintenance and reinforcement and particularly relates to an external prestressing reinforcing structure for an assembly type T-shaped beam. The external prestressing reinforcing structure comprises anchoring devices symmetrically installed on the top edge of a beam end web of the T-shaped beam and steering devices symmetrically arranged on the lower edges of webs at the 1/4 span position and the 3/4 span position. The anchoring devices and the steering devices are reliably connected through opposite-pulling anchoring bolts and steel sticking glue. Compared with the prior art, according to the external prestressing reinforcing structure for the assembly type T-shaped beam, steel components are installed quickly and conveniently, and the factory machining accuracy of the steel components is high; and through a prestressing steel strand applied to the reinforcing structure, the anti-bending and anti-shearing bearing force of the T-shaped beam can be effectively improved, a crack index is improved, development of a stress crack is restrained, and the bridge bearing force is improved by over 30%.