Halogen-doping TiO2 (X/TiO2) have been prepared through a mild hydrothermal route. Using X/TiO2 as the photocatalyst, photodegradation of phenol was observed both in freshwater and seawater. The degradation velocity of phenol in seawater is smaller than it in freshwater. The phenol degradation is influenced by the photocatalyst dosage and pH of seawater. The chemical reaction of the photocatalytic degradation phenol is the zero order reaction. The influence of phenol initial concentration on its degradation velocity is small.