Abstract: The flatness of the lower core support plate and the position of the fuel alignment pin holes were found deviated from the design requirements due to the heat treatment distortion during the manufacturing of the reactor vessel internals for the Haiyang Nuclear Power Plant Unit 1. The designer provided the treatment proposal and the repair plans after the cause analysis. This paper focuses on the deviations of the lower core support plate for Unit 1and describes the causes of the deviations. The repair plans and repair progress are also presented in this paper.