Provided is a pre-tensioned prestressed composite beam, which is an I-
shaped beam composed of H-shaped steel and concrete, the web plate of the H-shaped steel is provided with trapezoidal holes (14) at intervals, the upper
flange and the lower
flange of the H-shaped steel are welded with shearing nails, the outer periphery of the lower
flange is enclosed with concrete to form a steel-concrete lower flange (4), and the inside of the steel-concrete lower flange is embedded with prestressed steel twisted wire by pretensioning method. The manufacturing method of the composite beam is that: a steel plate is
cut into two tooth-shaped plates along tooth-shaped line to be respectively as the trapezoidal hole plates of the H-shaped steel flange, the trapezoidal hole plates are welded with
steel plates to form the web plate, the web plate is welded with the upper flange and the lower flange to form the H-shaped steel (1) having trapezoidal holes, the H-shaped steel is put on a base surface with the lower flange downward, the two sides of the lower flange are provided with side molds, a
stirrup (7) is arranged and steel twisted wires (3) are longitudinally fastened between the two side molds, the steel twisted wire is tensioned to tensioning state, the concrete for enclosing the H-shaped lower flange is poured and tamped between the two side molds, the steel-concrete lower flange (4) is formed after demolding, and the steel twisted wire at tensioning state is loosened after the concrete reached to predetermined strength and is
cut off at predetermined position. The invention is suitable for beams of buildings.