The invention belongs to the field of water treatment, and provides a method for reducing the comprehensive toxicity of water by combining ultraviolet light and free chlorine. According to the method, by combining ultraviolet light and free chlorine, the comprehensive toxicity of water can be effectively reduced, and the problem that the comprehensive toxicity of water can be increased in the chlorination process is solved. The water treatment method includes the steps that free chlorine is added into water to be treated, and meanwhile light irradiation is carried out, wherein a stirring state is kept in the water treatment process, the water to be treated is source water, filtered water in drinking water plants, sewage, ground water, industrial wastewater and the like, and free chlorine is chlorine gas and/or pypocholoride. Chlorine is excited with light irradiation to generate hydroxyl radicals and chlorine radicals with a strong oxidizing property to reduce the comprehensive toxicity of the water, and the method has the advantages that the efficiency of degrading toxic substances is high, agents are saved, operation is easy, and use is safe. After treatment is carried out with the method, the comprehensive toxicity of the water can be effectively reduced, and water quality safety can be ensured; the method has good application prospects.