The word "Cheng Kuo" refers to the outline of a city, also as the city wall area. The city wall, as an important defensive facility for ancient cities to resist foreign invasion, formed the overall outline of the city. The city moat is the river that surrounds the city wall. Excavate the moat, the excavated soil can build the city wall. The development and evolution of them not only affected the material space form of the surrounding areas, but also was closely related to people's lives. The city gate is the most important node space in the city wall area. As the entrance of the city wall connecting the inner and outer spaces of the city, the city gate plays the role of organizing traffic, military defense, city flood control and symbol and so on, and is also the main place where a large number of crowd activities occur within the range of the city wall area.