Based on the fracture network model and the cubic law of a single fracture with laminar flow, a method suitable for calculating hydraulic-head distribution and flow behaviors in fractures was developed. The method regards the rock matrix as an impermeable medium, and groundwater only flows in the network formed by the fractures and faults. The equivalent porous medium approach can be used to consider fractured or fault zones in the traditional analytical methods. The proposed approach assumes that the discrete fractured aquifer behavior is equivalent to porous media behavior and, therefore, any fractured or fault zones can be considered using a layer with much higher hydraulic conductivity than that of the intact rock. A case study in Jiangsu Province, China, was employed to verify the applicability and effectiveness of the method, and the influences of fracture orientation and tunnel slope on water inflow were evaluated. The method was applied to the prediction of water inflow to tunnels in the Liyang pumped-storage power station, and the water inflow calculated with this method was compared with the observed inflow. The results show that, compared with the traditional methods, the proposed method incurs only small errors and fits measured values well. It can be applied to the prediction of tunnel inflow in fractured rock mass, especially in areas where the permeability of fractures and faults is much greater than that of the rock matrix.