The invention discloses a square hole cutting device. The square hole cutting device comprises a shell and cutting pieces, wherein the shell is of a rectangular structure, a cavity is formed in the shell, four strip-shaped through holes are formed in the bottom of the shell, the four strip-shaped through holes are distributed in sequence so as to form a square structure, the four cutting pieces are of fan-shaped structures, the upper ends of the cutting pieces extend into the corresponding strip-shaped through holes, the curved surface ends of the cutting pieces protrude from the shell, and cutting sawteeth are formed on the curved surfaces of the cutting pieces; swing mechanisms which are used for driving the cutting pieces to swing from left to right in the extension directions of the corresponding strip-shaped through holes are arranged in the shell. The square hole cutting device has the advantages of the compact structure and simplicity in operation, the site requirement is low during use, and the technical requirements on operating personnel are low; compared with flame cutting, the use cost is low, and the use safety is high.