A steel plate and concrete composite structure reinforcing method for a positive bending moment area is characterized by including steps: firstly, treating the concrete surface of an original concrete beam bottom plate (5); secondly, embedding rebar (7) into the original concrete beam bottom plate (5); thirdly, making self-compaction concrete pouring holes (6) on the original concrete beam bottom plate (5); fourthly, making a steel plate (9), and welding cotters (8) and corrugated steel plates (14) to the steel plate (9); fifthly, setting up counter-top supports (2) and demounting counter tops; sixthly, binding a reinforcing mesh (10) and mounting the same in place; seventhly, applying structural adhesive on the steel plate (9) and scattering fine sand; eighthly, mounting and leveling the steel plate (9) at a designed position and pre-stressing the steel plate (9) through tension prestress of pre-mounted equipment; ninthly, agitating and pouring self-compaction concrete; and tenthly, releasing the prestress to demount the corrugated steel plates (14) and the counter-top supports (2), and performing concrete curing and demoulding to form the reinforced combined structure of the steel plate and the concrete in the structural positive bending moment area. The novel construction technique of reinforcing the positive bending moment by the steel plate and concrete composite structure comprehensively takes advantages of composite structure reinforcing, self-compaction concrete and corrugated steel plate, and the reinforcing method is widely applicable to reinforcing of positive bending moment areas of concrete box beams, T-beams, hollow plate girders, ordinary reinforced concrete beams, prestressed concrete beams and wide in application prospect.