The human-environment relationship has always been a research topic of sustainable development. In the past century, many theories about the human-environment relationship, such as environmental determinism, possibilism (probability theory), adaptation theory, cultural landscape theory, and human-environment harmony theory, have been put forward. These theories have reflected the dynamic change of the relationship between human and the natural environment, and advanced human understanding on nature. In the past 30 years, few breakthroughs have occurred in the studies on the human-environment relationship until the 'Two Mountains' theory ('Clear waters and green mountains are as valuable as mountains of gold and silver', or 'lucid waters and lush mountains are invaluable assets') was put forward by President Xi Jinping. The 'Two Mountains' theory is a new theory of the human-environment relationship based on the general trend of world development and the difficult practice in the past 70 years since the founding of the People's Republic of China. It is a qualitative leap in the development of the human-environment relationship theory, and has resonated with the requirements of the times from human-environment separation, human-environment mutual respect to human-environment integration. Furthermore, it has provided Chinese wisdom for the development and innovation of the human-environment relationship theories in the world. From a scientific perspective, the 'Two Mountains' theory contains a rich philosophy about the evolution of the human-environment system, and has interpreted the methods and paths of achieving the intrinsic unity, mutual promotion and coordinated symbiosis between the human development and environment protection. It has inherited and carried forward the traditional Chinese thought of the 'unity of man and nature', and expanded and deepened the Marxist dialectical relationship between man and nature. Enriching and innovating the Xi Jinping Thought on Ecological Civilization in the new era, it has profoundly revealed the basic laws of economic and social development, and laid the theoretical foundation for the construction of a 'modernization characterized by harmonious coexistence between man and nature'. From the perspective of the value of the times, the theory meets the requirements of the national 'five in one' overall layout, and demonstrates the implications of the human-environment relationship from philosophical, economic, social, ecological, and cultural dimensions. It is an important guide for the construction of a beautiful China in the new era. Additionally, the 'Two Mountains' theory enriches and develops the theories of the human-environment relationship in geography and is worthy of in-depth exploration and promotion by scholars from multiple fields. [ABSTRACT FROM AUTHOR]