Species sensitivity distributions (SSD) method was used to assess the acute ecological risk of four commonly-used organophosphorus pesticides (diazinon, parathion, fenitrothion and malathion) to freshwater organisms. The acute toxicity data (LC₅₀) were collected from ECOTOX database and SSD curves were fitted based on BurrⅢ function. The acute ecological risks of the organophosphorus pesticides and the sensitivity of vertebrate and invertebrate (including fish, crustaceans, insects and spiders) to these pesticides were compared by the hazardous concentrations for 5% of the species (HC5) and the potential affected fraction (PAF). The joint ecological risks of the organophosphorus pesticides in the Yellow River, Jiulongjiang River, and Wuxiaochuan River were also analyzed. The following results were obtained:1) by comparing the HC5 and PAF values, the toxicities and ecological risks of the organophosphorus pesticides to invertebrates were significantly higher than those to vertebrates, and the largest toxicities and ecological risks were found to crustaceans, while the minimum to fish. 2) It was found by comparing the SSD curves that, in case of the log-transformed concentration less than 3.5 μg/L, the ecological risks of four organophosphorus pesticides to invertebrates were significantly higher than those to vertebrates; on the contrary, in case of the log-transformed concentration larger than 4.5 μg/L, those to vertebrates were higher. 3) In the vast majority of exposure concentrations, invertebrates were more sensitive to the organophosphate pesticides than vertebrates. Under lower exposure concentrations, crustaceans were more sensitive to the organophosphate pesticides; while, under higher exposure concentrations, insects and spiders were more sensitive. 4) The PAFs and multisubstance PAFs(msPAFs) of parathion and malathion to the freshwater organisms in the Yangtze River, Jiulongjiang River, and Wuxiaochuan River were less than 0.5%, which imply that their ecological risks were very low.