Sustainable development of ecology has become a major issue for the socio-economic development. As the environmental protection and ecological issues become more and more prominent, it is urgent to conduct an in-depth exploration and analysis of sustainable development of ecology. Therefore, the harmony theory was applied to construct an indicator system based on five harmony systems, which are society, economy, water ecology, water resources, and water environment. 22 indicators were selected for the analysis of the water ecological sustainability of the Yellow River Lanzhou. The results show that the sustainable development capacity of water ecology in Lanzhou section of the Yellow River has been increasing year by year. The sustainable development of water ecology was classified as level Ⅴ-extremely unsustainable from 2010 to 2012, level Ⅳ - unsustainable from 2013 to 2014, level Ⅲ-almost unsustainable from 2015 to 2016, and level II-generally sustainable in 2017. In addition, it has not yet reached the optimal stage. The sustainable development of water ecology in Lanzhou section of the Yellow River is facing great challenges, it is necessary to strengthen the environmental protection and improve the ecological carrying capacity so as to improve its sustainable development capacity.