With the continuous expansion of the city scale, the traffic demand in the core areas of the mega cities is strong, and the structural defects of the road network in the core area lead to the objective contradiction between the traffic demand and the road supply. By analyzing the connotation of urban core area, the land development characteristics and typical traffic problems of urban core area are studied and judged, and the planning strategy of underground road in the urban core area is put forward. Finally, taking the planning and design of the underground road in Yizhou Avenue in High-tech South District of Chengdu as an example, the planning and design schemes of underground roads in urban core area are formulated in order to provide the reference for the development of underground roads in the megalopolis core areas.