Abstract: No.1 generator unit of Taoyuan Hydropower Station has been put into operation for 15 months. As the upper flow deflector of the generator was found in Class-C overhaul to have detached from the generator and fallen into the upstream flow channel, the project owner asked specialists in related fields to conduct a field investigation to analyze the cause of the accident. Considering the economic loss of the project owner and the treatment duration, the optimal treatment scheme was selected through repeated and meticulous research and analysis. After the repair work, the unit was restored to stable operation, which proved the satisfactory effects of the treatment. The background of the accident, the inspection results of the interior of the flow channel, the cause analysis of the accident, the process of designing and determining the treatment scheme, and the treatment procedures are introduced in details.