The invention discloses an adjustable assembled L-shaped cast-in-situ cast-in-place formwork steel back corrugated for reinforcement and an implementation method, belonging to the technical field of building formwork support and reinforcement. It includes the inner corner back flute assembly and the male corner back flute assembly, the inner corner back flute assembly includes a first adjustment back flute assembly, a second adjustment back flute assembly and a first connection assembly, the first adjustment back flute assembly The assembly and the second adjustment back flute assembly are detachably connected through a first connection assembly, and the male corner back flute assembly includes a third adjustment back flute assembly, a fourth adjustment back flute assembly and a second connection assembly, and the third adjustment The back flute assembly and the fourth adjustment back flute assembly are detachably connected through the second connection assembly, and the first adjustment back flute assembly, the second adjustment back flute assembly, the third adjustment back flute assembly and the fourth adjustment back flute assembly are all Vertical adjustment. The production is simple and economical, the operation is convenient, the vertical direction can be adjusted, the reliability is high, the construction period is saved, and the quality is guaranteed at the same time.