Abstract: The harmonious co-existence of man and nature is an important element of the construction of ecological civilization, and an important approach to solve the problems related to urbanization and urban ecological environment. Facing the demand of ecological security barrier protection and green and low-carbon transformation and development of cities and urban agglomerations, the author has sorted out the evolution of the connotation of eco-cities and the current situation of urban ecosystem observation, studied and constructed an observation index system for eco-city construction based on the harmonious coexistence of man and nature, including 28 indexes in four aspects: urban ecological security pattern, biodiversity protection, human living environment health, and green transformation and development. From the three dimensions of national policy guidance, local practice innovation and theoretical research and exploration, combined with the practice of eco-city construction in China, the study proposes a path to enhance the functions of eco-city, with a view to providing a theoretical basis and decision-making reference for the formulation of indicators and evaluation standards for national environmental protection model city construction in the new era.