To satisfy the huge energy demand of China, a rapid development rate of hydropower system was undertaken over the past decades. Currently, thousands of hydropower reservoirs with a total installed capacity of more than 330 GW have provided approximately 20% of China's gross electricity generation, ranked number 1 in the world. Besides, it is foreseeable that in the coming decades, the same development speed of hydropower will be maintained in order to effectively handle the increasing environment and energy problem. The dimensionality problem caused by booming system scale, unprecedented development speed and operational complexity are posing a giant challenge to the operation of large-scale hydropower system in China. Thus, after giving an overview of China's large-scale hydropower system, this paper deeply analyses the key operation characteristics leading to the dimensionality problem and highlights the possible dimensionality reduction strategies to sharply alleviate the optimization difficulty, providing necessary technical support to achieve the goal of energy conservation and emission reduction of China. To sum up, this paper could be a good and inspiring example, contributing to the sustainable development of worldwide countries with a high proportion of hydropower integration. (C) 2019 Elsevier Ltd. All rights reserved.