Based on the experience and facts of the reasonable degree of the size, density and intensity of the international megacities, the reasonable interval standards of people, space and ecology derived from the theory of human needs for a comfortable living environment, the urban size density and intensity interval standards derived from this, combined with the national conditions of China, such as large population and small construction land, to determine the reasonable interval of the size, density and intensity of high-quality development of China's megacities. To benchmark the development facts of China's megacities, find the problems of their size, density and intensity and their adverse effects on high-quality and healthy development, and put forward countermeasures and suggestions for building China's high-quality megacities.