Abstract: The photocatalytic oxidation of organic compounds using ultrafine semiconductor powder has been one of the most active areas for environmental problems.It is important from the viewpoint of practical applications to develop a simplified kinetic model suitable of representing the very complex mechanisms of photocatalytic oxidation.In the present paper,kinetic analysis is carried out for gas-solid photocatalytic reaction,and a kinetic model is developed.The theoretical results show that the rate of gas-solid photocatalytic reaction is proportional to the light intensity ( I ₀) under low UV light intensity, proportional to the square root of the light intensity under medium UV light intensity,and independent of I ₀ under extremely high UV light intensity.Photocatalytic reaction could be simply decomposed as three continuous processes as follows:photon transfer step, surface action step,and diffusion step.A novel gas-solid photocatalytic reactor is designed,and trichloroethylene is selected as the testing substance.The experimental results show that photon transfer step and surface action step are verified for gas-solid photocatalytic oxidation on nano-TiO₂ powder.