The Tennant method plays an important role in computing ecological flow. However, with river health protection and biodiversity maintenance being taken into account, the Tennant method exhibits some irrationalities. On the basis of two different understandings to the Tennant method, there are two approaches to setting ecological flow: one using the percent of the average annual flow and the other using the percents of the average flow in the same periods (the whole year being divided into several periods). Since the method is widely applied in China, the paper discusses and evaluates the applicability of the Tennant method and the two approaches for ecological flow computation preliminarily. The results show that there are some limitiations of the Tennant method in ecological flow evaluation,and the second approach is more reasonable than the first one.