Abstract: This paper proposed an ecological flow analysis method for medium and small rivers in water-rich areas of south China on the basis of runoff frequency and channel morphology. As an example, the method was applied to Yong’anxi basin in Taizhou city, Zhejiang Province. Baizhiao hydrological station was chosen as a control cross-section to analyze its ecological flow in different periods. The results showed that from April to September during the period of spawning and larval of fish, the control section’s ecological flow was 21.4 m3/s whereas from October to March, the ecological flow was 7.1 m3/s. The result was compared with the characteristic runoff of the Baizhiao hydrological station and the result calculated by Tennant method, based on the comparison this method was considered to be reasonable. The ecological flow calculated by this method not only has a certain concept of assurance rate, but also takes into account the hydro-habitat demand for the river, showing an operability in the condition with low ecological data.