Abstract: For the purpose of providing useful reference in aquatic ecological risk assessment, a detailed study in USA was conducted. The development process of aquatic ecological risk assessment methods in USA was introduced. The assessment methods developed from the quotient method to probabilistic ecological risk assessment, then to a tiered aquatic ecological risk assessment system which was introduced in this article in detail. Subsequently, the exposure assessment models used currently by USEPA such as GENEEC, PRZM and EXAMS were analyzed. At the end, works developed in USA were presented.