The invention discloses a wave loop I-shaped beam-steel concrete top plate-external prestressing combined T-shaped simply supported beam which comprises a wave loop I-shaped beam (1), a top plate (2) and an external prestressing cable (3). The wave loop I-shaped beam is adopted as a longitudinal beam, no web reinforcing rib is needed, and cracking caused by insufficient anti-shear capacity of a web is thoroughly avoided. The cross section of the top plate is heightened cross section, the weight is reduced by 30-40%, and no longitudinal gap is formed in the T-shaped beam; an upper flange plate and a lower flange plate of the wave loop I-shaped beam are flush with a top plate and a bottom plate of a beam body respectively, the role of a wave loop I-shaped beam stiff skeleton is brought into full play, and temporary facilities adopted during top plate pouring are simplified; the lower edge of the wave loop I-shaped beam is provided with the external prestressing cable, and therefore pre-camber used for counteracting dead load deflection does not need to be arranged on the simply supported beam; the simply supported beam is in a fish belly shape, the bending moment bearing capacity of the simply supported beam is ensured, and meanwhile materials can be saved. The T-shaped simply supported beam is high in construction speed, good in integrality, large in bearing capacity, and particularly suitable for city overpass bridges and projects with strictly-controlled underbridge disturbance and a short construction period.