Abstract: In the experiment of photocatalysis treatment for reactive-purple dye waste water，the index of decolorization rate of solid-phase was first used to replace the conventional decolorization rate of liquid-phase，and the optimum operation conditions of decolorization were as follows. TiO2 content 1g/L，waste water initial concentration 60 mg/L，air input 0.8 m3/h，lamp power 105 W. In experimental analysis of organic substance degradation，a new explanation about organic substance degradation was given by using several indices in combination.