Abstract: There have been serious defects in hydraulic structure through inspection under water in Qingtongxia Hydropower Station,which can be divided into two categories, one is abrasion dents on emergency gate floor of No.4 and No.11, together with that on floor of west tail gate slot of unit No.3; the other is cracks on sidewalls upstream of emergency gate. Those defects have severely influenced dam operation and safety. Thus, Qingtonxia Hydropower Plant has authorized Qindao Pacific Oceaning Co.,Ltd of carrying out scheme design and rehabilitation under water for defects and prominent effect has been achieved successful experience as well. The materials, apparatus and construction technique adopted in treatment under water are introduced.