To study the bending performance of prestressed steelbamboo composite I-shaped beams, 12 prestressed composite I-shaped beams were designed and manufactured for bending tests, considering prestress loads, prestressing schemes, and loading schemes as basic parameters. The experimental phenomenon was observed, and failure characteristics were analyzed during the test. The influences of different parameters on the load-bearing capacity, strain distribution, and deformation performance were explored, and an approximate formula for the bearing capacity of the prestress composite beam was proposed. The results indicated that the prestressed composite beams have relatively good performances from the perspectives of combination effect, deformation characteristic, and bearing capacity. Failure modes of tested specimens were mainly owing to the bamboo flanges damage and the local buckling of steel plates. With the technique of prestress and the increase of prestress level, the deformation performances can be improved effectively, as well as the load-bearing capacity considering the same deflection situation. Moreover, the improvements can be more significant with the two-point prestressing scheme. The mid-span strain distribution of prestressed composite beams conforms to the plane section assumption, and the neutral axis moves down with the increase of the prestressing level. Finally, the bearing capacities based on the theoretical calculation matched well with the experimental results, which showed the applicability of the proposed methods.