The groundwater level in the deep foundation pit project close to the river shows a dynamic characteristic of long-term low water level but high water level during flood season. Foundation pit dewatering leads to the complexity of the seepage field in the surrounding stratum environment, destruction of enclosure structures, accidents include piping and instability at the bottom of the pit. Therefore, this paper simulated the excavation-precipitation process of deep foundation pit project based on the HS-Small constitutive model, analyzed the sensitivity of precipitation influencing factors (precipitation depth, mode, rate and water stop curtain) to the surrounding environment deformation and their relationship. Compared the analysis results with the measured results, it can be found that the settlement of the top of the foundation pit, the soil outside the pit and the surrounding buildings gradually increases, and the dewatering has a more obvious influence on the deformation during the excavation and dewatering of the foundation pit; Fractional precipitation can effectively reduce the settlement deformation of surrounding buildings and ground surface; It is recommended that the dewatering depth of foundation pit should be controlled within 0.5-2.0 m below the bottom plate; The precipitation rate has a relatively small impact on the total settlement of the surrounding environment, but has a great impact on the settlement rate. When the precipitation rate reaches the optimal value, it is beneficial to the stability control of the foundation pit. The embedded depth of water-proof curtain in this project is more than 30 m, which has no obvious effect on controlling the settlement of surrounding buildings. The research results can provide reference for the dewatering design and construction of similar deep foundation pit projects closed to the river.