Abstract: Some appropriate assessing methods for instream ecological flow or environmental flow requirements are established after many years research.Each method differs in its data requirements,procedures for selecting flow requirements,and ecological assumptions.An applicable method is chosen based on the current information and the goals.Four categories of the common methods,namely,hydrological index methods,the hydraulic methods,the holistic methods,and habitat methods,available for assessing instream environmental flow,are reviewed according to their applicability.