Large scale water/mud inflow occurs at the face of No. 1 Dayaoshan tunnel on Wuhan～Guangzhou passengerdedicated railway when the construction of the tunnel reaches DK1909+624 and enters F6 fault. It is observed that a large fillingtype waterrich karst cave exists on the right side of the tunnel. The construction of the tunnel is carried out strictly in accordance with the principle of “water probing, pregrouting and installing forepoling pipe roofs, which are followed by tunnel excavation, radial compensation grouting and quick lining”. The concept of “drainage assisted by waterproofing” is adopted. For the sake of these principles and concepts adopted, the construction of the tunnel passes the karst cave with safety and high speed.