The invention belongs to the technical field of building construction, and provides a stair corner protection tool. The stair corner protection tool comprises a stepping corner, a corner guard plate,a fixed support plate and a connecting piece, wherein the stepping corner is provided with a stepping surface, the corner guard plate is L-shaped, two ends of the top surface of the corner guard plateare provided with hollow pipes, two ends of the outer side surface of the corner guard plate are provided with circular sliding strips, the fixed support plate is L-shaped, a hollow circle is arranged on the bottom surface of the fixed support plate, a circular slideway is arranged on the outer side surface of the fixed support plate, and the hollow pipe is connected with the hollow circle through a buckle. Compared with the prior art, the stair corner protection tool has the advantages that the corner guard plate is laid on the stepping corner, the fixed support plate is used for splicing, the hollow pipes are inserted into the hollow circle, the circular sliding strips and the circular slideway are connected with each other, the stepping corner is wrapped in the corner guard plate, if the length of the corner guard plate cannot meet the length of the stepping corner, the connecting piece can be used for splicing, and the stair corner protection tool is simple in structure and convenient to disassemble and assemble and can be recycled.