The invention relates to a shredding device for a maize harvesting machine impurity removal draught fan. The shredding device comprises a discharging opening, a bolt, a nut, a gasket, a fan blade seam, a draught fan shell seam, an axle nut, an axle gasket and a shredding blade. The discharging opening and the fan shell seam are connected through the bolt, the nut and the gasket. The fan blade seam is installed inside the fan shell seam. The fan blade seam is composed of four rotating vanes, four rotating blades and a rotating shaft, the four rotating vanes are uniformly arranged on the rotating shaft in the circumferential direction, the four rotating blades are installed on the four rotating vanes respectively, one end of the rotating shaft penetrates through a lower flange in the fan shell seam to be connected with a motor, the other end of the rotating shaft is provided with the shredding blade, and the shredding blade is fixed through the axle nut and the axle gasket. Due to the fact that maize straw and other impurities are cut through the shredding blade and the rotating blades two times, particles become finer and smaller, the field returning effect is better, the impurity removal draught fan is not likely to be blocked, the number of impurities entering a peeling machine is small, the service life of the peeling machine is prolonged, and economic benefits are created.