The distribution and ecosystem risk of 16 polycyclic aromatic hydrocarbons (PAHs) in the Luan River, China, has been investigated. summation operatorPAHs levels ranged from 37.3 to 234 ng L(-1) in water, from 20.9 to 287 ng g(-1) in sediment and from 36.9 to 378 ng g(-1) in bank soil, respectively. A method based on toxic equivalency factors (TEFs) and risk quotient (RQ) which can be used to assess the ecosystem risk of summation operatorPAHs sensitively and accurately was invented and a new ecosystem risk classification of summation operatorPAHs was suggested. The results indicated that the PAHs in aquatic environment of the Luan River resulted in low ecosystem risk and at S9 the ecosystem risk of PAHs in water was moderate. Low and moderate molecular PAHs presented much more ecosystem risk than high molecular PAHs in the Luan River basin and the mean ecosystem risk in water was higher than that in sediment and bank soil.