Abstract: The top drive of an offshore drilling platform is imported. After 5 years of use, bearings of the top drive gear box run on the outer ring, and the bearing seats are worn. Since there are no technical parameters of the gearbox, the paper explains the measurement and analysis process of the technical parameters of the gearbox, and determines the technical parameters of the gearbox according to the technical standards. Besides, the technical parameters are optimized when repairing the gearbox, and the tolerance matching parameters with the bearing seat are improved, which solves the problems of bearings running on the outer ring and the bearing seat wear. It has improved the carrying capacity of the equipment, achieved independent repair of imported equipment and made useful attempts to reduce equipment failures and extend equipment life.