The development of ecological civilization in China based on the economic–social–natural complex system

China is making great efforts to build an ecological civilization. To reveal the effectiveness and spatial characteristics of the ecological civilization development in China, we constructed an Ecological Civilization Evaluation Index (ECI) based on the economic-social-natural complex system. We evaluated the development level of the ecological civilization in China from 2004 to 2020 and discussed the coupling and coordination relationship between subsystems. We found that the ecological civilization of China has achieved remarkable results. The relationship among the three subsystems has been improved to some extent, but the high-quality development of the economic system still requires effort. The development level of the ecological civilization in China presents spatial heterogeneity. From east to west, 30 provinces can be classified into four different types of development. On the whole, the development of China’s ecological civilization has provided experiences for the world.