The quantitative relation between deactivation and the adsorbed NO3- concentration was studied by intentionally controlling the adsorbed NO3- concentration. The photolysis ability and adsorption ability of TiO2 was detected against acetaldehyde as a probe. The results show that when the adsorbed NO3- concentration reaches 4.24wt%. photolysis ability decreases 50%; when the adsorbed NO3- concentration is 10.50wt%, the TiO2 adsorption ability decreases 50%; after water overflow-cleaning 2 h, the NO3- is removed by 98% and the photocatalytic activity is regenerated.