Abstract: As for the water inflow in water-rich tunnels, it follows the treatment principle that "priority is given to blocking, and waterproof and drainage are combined". The rationality of drainage system is a key factor of the safe construction and good operation of tunnels. First the tunnel drainage system is analyzed to reveal its working principle, and then the finite difference software FLAC 3D is adopted to carry out the 3D fluid-solid coupling simulation for different spacing conditions of circumferential blind drainage pipes in the water-rich fault zone of Hongtu extralong tunnel, and the seepage pressure, rock bolt stress and water inflow are analyzed to reveal the volume and distribution characteristics of the plastic zone. The study result shows that the pore water pressure on the support structure along the tunnel axis is roughly periodically distributed, with the period approximating to the longitudinal spacing between circumferential blind drainage pipes; increasing the density of circumferential blind drainage pipes, it could reduce the stress on the support structure and the volume of plastic zone and also increase the amount of tunnel drainage; with an increase in the spacing between circumferential blind drainage pipes, the plastic zone of grouting reinforcement ring first appears in the area where the surrounding rock is good and appears in the fault area at the latest; the reinforcement effect of anchor bolts in the fault area is poor, so the circumferential spacing between steel ribs can be reduced to improve the structural rigidity and make the axial stress on the grouting reinforcement ring more reasonable. After due consideration of various factors, it is recommended that regarding the studied tunnel project the spacing between circumferential blind drainage pipes in the fault area should be 3 m and the spacing in the areas near the fault should be 4 m.