The TiO2 photocatalytic reaction which is used for wastewater and exhaust treatment processes has been studied and developed. The organic compounds could be oxidized completely into the simple, non-toxic products such as CO2, H2O, etc., when using TiO2 which is lighted by UV source. The study shows that V-doped TiO2 can absorb visible light so the authors can expand scope of application of TiO2. The authors have used this catalyst to decompose TNT which is very resistant and toxic in wastewater. The results show that 0.3 percent to 0.5 percent V-doped TiO2 nanopaticles can decompose almost completely TNT after 480 minutes lighting by incandescent lamp and sunlight. The concentration of TNT is less than 0.5 mg/L of TCVN 5945-2008.