Abstract: Deep foundation pit dewatering not only wastes groundwater resources, but also causes urban land subsidence. The statistical data of foundation pit drainage in the region is of great significance to the study of regional land subsidence. However, in the past, there was no monitoring drainage data during the dewatering construction of deep foundation pit, and only data such as foundation pit area, excavation depth and rough location information can be obtained. We need to use the existing data to estimate the drainage of deep foundation pit. In this paper, we determine the dewatering target aquifer by determining the geological zoning of deep foundation pit engineering, estimate the safe drawdown of foundation pit aquifer system through the three-dimensional geological information of the zoning, and estimate the drainage of foundation pit by analytical method and numerical method. Taking Shanghai as an example in 2020, it is estimated that the overall drainage of foundation pit reached 9.71 million cubic meters, the minimum drainage of single foundation pit was 28.8 cubic meters, and the maximum drainage reached 778000 cubic meters. The estimation method proposed by us can provide a reference basis for the historical analysis of urban groundwater resources and the correlation analysis of land subsidence.