Abstract: Titanium dioxide/multi-walled carbon nanotubes(TiO2/MWCNTs ) was prepared by sol-gel method, with the quality ratio of 3:4 and the surface average pore size of 5.724 nm. This composite materials were then applied in the photocatalytic degradation of dimethoate. A series of affecting factors were studied, including the difference of light sources, the illumination time, the initial concentration of dimethoate, the adding quantity of composite materials, the solution temperature, etc. The results showed that the degradation rate of dimethoate was 80.7% under the conditions of the solution temperature at 25 ℃, the illumination time of ultraviolet light for 30 min, the initial mass concentration of 5 mg/L, the composite additive amount of 0.25 g/L and ultraviolet light and the maximum adsorption capacity of TiO2/MWCNTs is 16.15 mg/g. Under the same conditions, but using natural light instead of ultraviolet light, the catalytic degradation rate was 79.2%, which had little difference compared with the rate using ultraviolet light. However, under the same conditions, the catalytic degradation of dimethoate using TiO2 under ultraviolet light is lower than TiO2/MWCNTs by 33.1%. Therefore, natural light can be used in the adsorption experiments instead of ultraviolet light, and employing this technology under natural conditions can effectively degrade the environment pollution of dimethoate.