In order to understand the toxic effects of the pollution by organophosphorus pesticide as acephate on the local aquatic sensitive species as Scenedesmus obliquus,under laboratory conditions,based on the static toxicity test,the acute toxic effects of acephate on Scenedesmus obliquus for 96 hours were investigated in this paper.And based on the acute test,the chronic experiments including the 14 days changes of chlorophyll a,soluble protein and MDA in Scenedesmus obliquus were analyzed.It shows that:the 96 h EC₅₀of acephate is 482.9 mg/L,which belongs to the low-toxic pesticide and the growth of Scenedesmus obliquus could be promoted with 1 mg/L of acephate;no significant effect is showed on the photosynthesis of Scenedesmus obliquus,but the toxic effects are exposed by acephate through interfering the algae's metabolic activities and causing membrane lipid peroxidation;the soluble protein and MDA could be used as valid biological markers for evaluating the toxicity of pesticide.The results in this paper could be considered as the theoretical basis for protecting local aquatic sensitive species and establishing the criterion on safe use of pesticide.