The invention relates to an assembly-type section steel cantilever protective shed which comprises a base and a shed body. The base and a building floor are arranged in parallel, one end of the base is supported on a main structure beam of any building floor, the other end of the base stretches out of the building floor, the base comprises two or more I-shaped steel main beams, a plurality of reinforcing steel bar cross beams are perpendicularly connected between the two I-shaped steel main beams, and a steel plate is laid on the reinforcing steel bar cross beams. A plurality of supporting steel pipes are perpendicularly welded onto the I-shaped steel main beams at intervals, a main steel pipe is welded onto the supporting steel pipes in a supported mode, and a scaffold board is laid on two main steel pipes which are supported on the two I-shaped steel main beams respectively. The shed body comprises a shed body framework and a protective net. The shed body framework comprises a scaffold and framework steel pipes, wherein the scaffold is supported at the near ends of the I-shaped steel main beams and the near end of the building floor, and the framework steel pipes are perpendicularly welded to the far end of the building floor. The protective net is arranged between the scaffold and the framework steel pipes and arranged between every two framework steel pipes in an expanded mode.