This paper introduces the definition, the features, and advantages of megalopolis according to the book called Urban Design Since 1945, and compares the definition, features, advantages and problems of the megalopolis mentioned in the book with Beijing-Tianjin-Hebei(BTH) urban region. Although megalopolis solves different urban problems for regions, it still faces different problems. In the future, urban planners should pay attention to the sustainable development of urban ecology and make rational use of various resources.