Underpass tunnel provides more smooth and convenient traffic conditions for improving the quality of urban development. Its overall design not only affects the traffic function of the road network, but also restricts the spatial layout of other underground projects, and is of great significance for the overall utilization of underground space resources. Taking the Nanjing International Road Tunnel Project as an example, the complex engineering environment around the underpass tunnel is analyzed. The key points of the overall design of the underpass tunnel are summarized. The technical strategy for the cooperative design of related underground projects is put forward. The above can provide the reference for the related projects under the similar conditions.