Abstract: It is a challenge to accurately characterize the irregular geological bodies and underground structures such as inclined faults and inclined tunnels during the numerical simulation of tunnel water inflow prediction, and the prediction generally assumes that the tunnel excavation is completed instantaneously without considering the construction progress. A dynamic prediction method for tunnel water inflow based on precise characterization of complex geometric bodies was proposed by addressing the non-self-intersection and watertight issues required in the coupling process of three-dimensional (3D) geological models and 3D groundwater numerical models. Specifically, a sealed boundary interface of inclined tunnels, shafts, inclined faults and irregular geological bodies is firstly constructed in 3D geological modeling software. The inclined tunnels and shafts need to be segmented according to the excavation progress, and then a 3D geological model is established. Subsequently, the 3D geological model data is imported into the 3D groundwater simulation software, Feflow, in ml file format. Then the fully unstructured grid function of Feflow is used to achieve the fine gridding of the complex geometric bodies. Finally, the tunnel boundary is set as a third type boundary based on the detailed gridding of complex geometric body in Feflow. Thus, tunnel water inflow can be predicted dynamically by setting the exchange coefficients and reference water heads with consideration to the tunnel excavation progress and construction techniques (such as grouting, lining, etc.). The method is applied to the calculation of water inflow in inclined tunnels and shafts in an underground project, with good practical effect.