The support replacement design of water tank foundation excavations should not only meet the safety and stability of the foundation excavations itself, but also take into account the construction convenience, construction period requirements, engineering economy and the water pressure test requirements of water tank. On the basis of summarizing the support replacement design of water tank foundation pit engineering in Nanjing soft soil area, this paper proposes a new method of using the buttress (or wall column) and internal vertical and horizontal wall plate of the main structure of the water tank as the support replacement system, which is applied to engineering practice to provide reference for similar design and construction.