Folding deformable sofa

The utility model relates to a sofa, and particularly relates to a folding deformable sofa. A seat cushion is rectangular, the seat cushion is provided with a step, and an L-shaped deformable back board is laid on the seat cushion; and one surface of the L-shaped deformable back board is attached to the side surface of the seat cushion, and the other surface of the L-shaped deformable back board and a step surface are integrally arranged to form a folding backrest; and one end, which is close to the side surface of the seat cushion, of the step surface is provided with a backrest clamping part. According to the structure, the seat cushion is provided with the L-shaped deformable back board; when the sofa is in normal use, a part of the backrest is clamped on the step, and the other end of the backrest is vertically attached to the side surface of the seat cushion, so that a cuboid backrest-free sofa is integrally formed; and when the backrest is needed, the L-shaped deformable back board is raised, the movable end is clamped on the backrest clamping part, so that the L-shaped deformable back board is swelled to form a backrest structure. The folding deformable sofa disclosed by the utility model can be folded and deformed and wide in applicability.