The invention provides a resistance-free square valve. The resistance-free square valve which is a valve without internal structures and resistance generation is particularly designed for a partition requiring position in a square dedusting air pipe and is applicable to long-term operation in dedusting pipelines. The resistance-free square valve comprises a square valve body with the section in a square structure, and the upper wall, corresponding to the rear of dust flow at a partition position, of the square valve body is provided with a rectangular notch. A rotating shaft is arranged at the position of a front end wall of the rectangular notch, a rotating end of a rectangular blade sleeves the rotating shaft, and the end, away from the rotating end, of the rectangular blade is a tail end. The tail end of the rectangular blade is positioned in an inner cavity of the square valve body and capable of rotating. Three sides of a non-rotating end of the rectangular blade are closely attached to corresponding inner walls of the square valve body under a closed state of the valve.