Chlorination disinfection by-products (CDBPs) exhibit adverse effects to human health and toxic organic compounds in source water contribute significantly to CDBPs due to their high activities. The distribution of CDBPs was investigated using phenol as a model of ionizable toxic organic compounds in the pH range of 6.0-9.0. Five chlorine substitution products, including 2-monochlorophenol (2-MCP), 4-monochlorophenol (4-MCP), 2,6dichlorophenol (2,6-DCP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (TCP) were detected quantitatively by HPLC and three oxidation products, including resorcinol, hydroquinone and catechol were identified by UPLC-MS/MS in chlorination process. It was found that total molar concentration of five chlorophenols was higher in alkaline media than in neutral and acid media. MCP (2-MCP and 4-MCP) were the dominant chlorophenols in acid media, while TCP and DCP (2,6-DCP and 2,4-DCP) were the main chlorophenols in neutral and alkaline media. These results demonstrate that pH plays an important regulating role in reaction pathway and species distribution of CDBPs in the chlorination of ionizable toxic organic compounds and the risk of chlorophenols is possible to be controlled in slight acid media in water disinfection.