Abstract: The long transmission shaft of anchor winch on a marine semi-submersible rig has many corroded pits after years of use.Since the anchor winch is an imported equipment and has no relevant technical parameters, the paper describes the measurement and analysis process of the technical parameters of the long transmission shaft and the bearing of windlass, and determines the technical parameters such as tolerances and dimensions of the long transmission shaft according to the technical standards. It is considered that the interference fit between the long transmission shaft and the rolling bearing is adopted, and the tolerance zone of the long transmission shaft is r6. The long transmission shaft and the sliding bearing adopt a clearance fit.The corroded pits of the shaft were repaired by laser welding, and the repaired shaft was ground on a grinder. The corroded parts of the shaft were repaired by iron plating. After the iron plating, the shaft was ground on a grinder, and the repaired shaft surface Ra=0.8 µm after processing was repaired. After assembly and trial operation, the anchor winch works normally.The research result fills the technical gap of the overhaul of long transmission shaft of anchor winch on marine semi-submersible rig, and has the corresponding reference significance for the overhaul of long transmission shaft of anchor winch on marine.