Abstract: Objective To study the photodegradation of dibutyl phthalate(DBP)in flowing water.Methods 4 kinds of flow velocity:25,65,110,190 ml/min.4 kinds of treatment:aerate O₃(to aerate the gas produced by O₃ generator,flow rate: 0.6 L/min,the following is same);ultraviolet(UV)radiation;UV radiation with aerate O₃(UV/O₃);UV radiation with aerate air(UV/air).The removal rate of DBP in water was determinated after photodegradation in existing catalyzer nanometer TiO₂ or not.Results Nanometer TiO₂ can promote DBP in water to photodegrate rapidly.The photocatalysis removal rate of DBP can reach 88.8% when flow rate at 190 ml/min.Aerate air didn't promote UV degrate.Sy nergetic effect existed in the photodegradation of DBP by UV and O₃.Conclusion DBP in flowing water can be effectively degr aded by TiO₂ photocatalysis.