The Communist Party of China (CPC) has in the people its roots, its lifeblood, and its source of strength. Ecological civilization is an integral part of the Five-Sphere Integrated Plan and the Five-Sphere Advancement of Socialism. Ecological civilization is a new form of human civilization written into Constitution of the People’s Republic of China and protected by the fundamental law, with the pursuit of the harmonious coexistence of human and nature as its core, and with its underlying value orientation adhering to a people-oriented development. Learning from the CPC’s century-old ecological civilization, including its germination, exploration, development, perfection, and maturity, especially in the new era, for the first time in the CPC’s century-old history, Xi Jinping Thought on Ecological Civilization is established, which specifically guides the theory and practice of ecological civilization. It is not only the inheritance and development of Marxist thoughts on the relationship between human and nature, but also fundamentally manifests its value of the supremacy of the people. The establishment of the people’s supremacy in the pursuit of ecological civilization under the leadership of the CPC differs from Western anthropocentrism or ecocentrism. It develops keen insights into important documents of people’s supremacy in the history of the CPC’s ecological civilization for the 20th century, which is of great theoretical and practical value to understand the spiritual genealogy of the CPC more completely, accurately, and systematically, to clarify the underlying value orientation of ecological civilization, to better learn and practice Xi Jinping Thought on Ecological Civilization in the new era, and to build a modernized society of harmonious coexistence between human and nature.