During the overhaul of a nuclear power plant, there are unfavorable factors such as heavy workload, tight schedule, and concentrated work. During the startup and shutdown of a nuclear power plant, it is a period of large-scale system isolation, release of isolation, online work activities, testing, water filling and exhaust, and system shutdown and startup by the operators. The time is tight and the operations are numerous, making it a high-risk period for human error among the operators. Lack of operating experience and familiarity with system equipment characteristics increase the probability of human error among the operators. This article analyzes the human error that occurred during the first overhaul of nuclear power plants in China, and proposes countermeasures and measures to reduce human error during the first overhaul of nuclear power plants.