Abstract: The flow path of the pre-site hydrogen cation bed combined with the mixed bed is generally applied in the fine treatment system to remove impurities in the second circuit of nuclear power plant. On the failure of the cation bed, it is necessary to regenerate with industrial hydrochloric acid. The deviation of the water quality of the steam generator of the power plant occurred in Unit 2 of Tianwan NPP resulting from the pollution of highly acidic positive resin in the fine treatment system. By analyzing the screening methods and the water quality characteristics of the organic-chlorine pollution, the qualitative detection method of organic-chlorine and the treatment measures after the organic-chlorine pollution were proposed.