The dye wasterwater has some unique features: high COD_Cr, high intensity of color, high salinity, hard to degradation, great changes in water quality and quantity and so on. It becomes oxidation resistant and anti-bio-degradable, which makes it difficult to be treated. The general aim of treatment is to remove COD and to decolor, which is more difficult. Color is the most important indicator to check whether the printing and dyeing wastewater treatment can meet the emission standards. With the traditional method of wastewater treatment to hydrophilic or water-soluble dye wastewater, the decoloring effect is not satisfactory. The biological decoloring is less effective, while the physical and chemical decoloring does cost much. This paper is to find a simple, economical as well as effective way of decoloring printing and dyeing wastewater. Photocatalytic oxidation can be done in an ordinary condition (normal temperature, atmospheric pressure), but with strong oxidizing ability, with a great speed and without secondary pollution. In the water treatment domain, the AOP technology is widely used in environmental protection. Currently TiO₂ is used as the photocatalytic oxidation catalyst, with the ultraviolet ray as the light source, mostly in a man-made form. Its use is limited because of its large energy consumption and poor efficiency in the utilization of solar energy. This study uses the near ultraviolet ray as the light source, AgCl as the catalyst, to reveal the effects of the dye concentration, the amount of catalyst, pH, the different light sources on the decoloring rate of reactive brilliant red K-2BP dye wastewater. The results show that with the dye initial concentration of 50mg/L, the concentration of catalyst 1000mg/L, and pH=4.0, the decoloring rate of the reactive brilliant red K-2BP dye waste water reaches 72.1％. Under the best technological conditions as indicated by the theory, the application of this system to the actual dye waste water may result in more ideal results. On the basis of the discussion of the various factors that influence the decoloring of the reactive brilliant red K-2BP dye wastewater with near ultraviolet ray-AgCl system, a dynamic equation for the degradation of the reactive brilliant red K-2BP is established, to analyze the degradation mechanism, and the structural composition of some replaced aromatic compounds during the K-2BP degradation process, as well as the reaction intermediate products and final products, and thus to trace its degradation routes. AgCl as a catalyst is similar in the catalytic oxidation mechanism to TiO₂, and the sunlight can be used as the light source, not just UV. This not only reduces the energy consumption, but also repeatedly uses AgCl. It opens a new way for the photocatalytic oxidation of degradation wastewater.