The invention discloses a photoelectric corrective mechanism adopting a rust-proof electric cylinder for a coil slitting machine. The photoelectric corrective mechanism comprises an unreeling roller, a support, guide tracks, a photoelectric sensor, the electric cylinder and a controller, wherein the electric cylinder comprises a corrugated expansion pipe connecting a bearing pipe and a thread bushing; and the photoelectric sensor comprises a cover plate, tubular supporting columns and screws arranged inside the tubular supporting columns. According to the photoelectric corrective mechanism, the deviation conditions of edges of coils can be detected constantly through the photoelectric sensor, the correction is carried out in time, the correction accuracy is high, and the working efficiency of the correction is high; screw rods are sealed through the corrugated expansion pipe, so that water is prevented from contacting the screw rods and causing corrosion and damage of the screw rods, and the failure rate of a correction device is decreased; the photoelectric sensor supports the cover plate through the tubular supporting columns, during installation, both the cover plate and a circuit board share the same connecting screws, the number of the screws is small, and the working efficiency for installation is high; and the sealing cover plate is fixed on the tubular supporting columns through screws, during manufacturing, threaded holes are not required to be formed in the U-shaped casing, and the manufacturing cost is low.