Rapid global urbanization has led to a series of issues such as climate change and sea-level rise. The solution to such problems ultimately comes down to resolution of the conflict between man and nature. The philosophy of ancient China and the West presented a nave holistic description of the relationship between humans and nature, and whereas the reductionism-centric approach of modern Western science has been unable to solve the real-world complexities. Cities, which can be considered as giant complex open systems, wherein the entire range of human nature can be founds, are places facing many problems. Urban development is a natural-adaptive evolutionary process. Introduction of complex adaptive systems in urban planning, combined with the seven basic characteristics of complex adaptive systems, divides the complex city system into physical subsystem and non-physical subsystem. We discuss the relationship between adaptive agents, the complexity of adaptive agent, and adaptation mechanisms. As an example, we examine mountainous city planning, produce an adaptive planning framework for mountainous cities, and apply this framework to the Urban Master Plan of Changting, Fujian Province. The results demonstrate that urban planning that is adapted to nature is an effective approach to sustainable urban development.