Abstract: Gadui Hydropower Station utilizes a water level drop of 756 m, in which the maximum water head of the pressure tunnel in front of the penstock plug is 406 M. After the first unit generates electricity, seepage occurs in the hill along the line in the initial stage of operation. When the tunnel was emptied, leakage occurs generally along the line, cracking and uplifting of local lining, shotcrete anchor and floor occur. Later, with the joint efforts of all parties involved in the construction, the characteristics of leakage and damage along the diversion tunnel were identified and targeted measures were taken to effectively control the leakage, eliminate the damage defects, successfully solve the problem of excessive leakage and safe and stable operation of the diversion tunnel.