Abstract: On-load tap-changer is one of the important components of the transformer. which is widely used in power system. According to statistics, the faults caused by the tap-changer account for a considerable proportion of transformers in operation. There are many on-load tap-changer lead connection parts, loose connections are the main cause of defects. so it is necessary to improve the quality level of installation and maintenance, formulate factory acceptance standards and maintenance process requirements, and ensure the safety of the transformer.