The phased implementation of narrow buffer zones in deep foundation pits is an effective way to control engineering risks, which has become more common in recent years. It is necessary to analyze and summarize the design and implementation process of such projects. This article takes the co construction zone of the "Nanjing Global Trade Plaza" and "Nanjing World Trade Center" projects located in the Hexi area of Nanjing as an example to introduce the implementation plan of synchronous construction of adjacent super large and ultra deep foundation pits with buffer zones first and then co construction of buffer zones under soft soil and water rich geological conditions. The focus is on explaining the technical measures taken according to local conditions to achieve smooth construction of narrow foundation pits in the co construction zone, protection of rail transit facilities, and economic feasibility of the project, especially when the basement structures on both sides have been completed. The implementation results are analyzed. Practice has shown that the design scheme and key technical measures adopted well embody the principles of "safety and reliability, economic rationality, technical feasibility, and convenient construction", and can provide reference for the design and construction of deep foundation pit projects under similar conditions.