The characteristics of water inflow in tunnels within a fault fracture zone were investigated in this paper. The model test was conducted to explore the influence of surface water and the effect of grouting on the water pressure distribution and inflow quantity in the tunnel. Water inflow was characterized by four stages—wet stage, dripped stage, gushed stage, and collapsed stage—based on monitoring of the inflow quantity. The rapid decrease in water pressure was observed before the collapse of the tunnels. Meanwhile, the critical thickness of the layer installed against the inrush (the “anti-inrush layer”) was studied in the model test; this layer varied from 2 to 6 cm under different conditions. It was found that the presence of surface water increases the water inflow and the minimum thickness of the anti-inrush layer, and that grouting may effectively decrease the water inflow and also affect the minimum thickness required for the anti-inrush layer. A numerical simulation was conducted, and it was found by comparisons with the model test and field investigation that good agreement was achieved.