A large number of ecological projects are used in the river and waterway regulation for the middle Yangtze River in recent years，and great ecological benefits are obtained. However，there is an obvious cyan-yellow line on the ecological bank slope according to field investigation. Aiming at this problem，we take Xinchang bank protection project and Taohuazhou bank protection project in the middle Yangtze River as examples，divide the bank slope into the cyan-green zone and cyan-yellow zone by the cyan-yellow line，analyze the distribution characteristics and the formation mechanics of bermudagrass，and determine the design control elevation of the cross-section by the cumulative frequency curve of water level. The results show that the elevation of the cyan-yellow line is closely related to the controlling of the Three Gorges reservoir. The elevations corresponding to the cumulative frequency of 45% and 80% are the design control elevations of the ecological bank protection section.