Under the influence of climate change and human activities,the contradiction between production and living and ecological water consumption in the lower reaches of Ganjiang river is increasing day by day.In this study,the Tennant method and ecological flow threshold method were used to calculate the ecological water requirement of the outer continent section,and wetted perimeter method based on the ecological protection objective of four fish was used for screening and comparison to determine the appropriate and relative appropriate ecological water requirement process in the lower reaches of Ganjiang river.The results show that the average annual optimum ecological water requirement calculated by Tennant method and ecological flow threshold method is 845.44 m3/s and 1 041.30m3/s respectively,accounting for about 40% of the annual average runoff for years in the outer continent section.The average annual optimum ecological water requirements are 626.60 m3/s and 561.16 m3/s calculated by those two methods respectively,accounting for about 27% of the annual average runoff for years in the outer continental section.It provides a basis for the reservation of the optimum ecological water requirements in the lower reaches of Ganjiang river.