Abstract: Leakage of concrete dam body affects the safety and durability of the dam. Based on the dam body leakage remediation of Longjiang hydropower station in Yunnan Province, the remediation of the dam is introduced in detail, and the remediation result is discussed. In order to find the possible leakage entrance, temperature tracing is applied for finding the range of leakage entrance, and then the specific leakage point is indicated by subaqueous extended check. Through subaqueous check, defects in the concrete dam body between the layers are detected. The main entrance points of leakage passage are located at elevation 832.00 m and 816.00 m in dam block 9^#, and 830.00 m and 808.00 m in dam block 10^#. Therefore, subaqueous remediation is adopted for the dam body, and leakage entrance is blocked from source. After the remediation of the dam body, leakage decreases from maximum 74.85 L/s in recent years to 6.04 L/s under normal water level. From the subaqueous check of the dam body before remediation, the seams between layers are identified as the main way of leakage in the concrete dam. The seams between layers are produced during the whole construction process. Hence, it is necessary to enhance the quality control during construction process to ensure the bond of each layer in concrete. Above all, partial leakage defect could be solved by the leakage subaqueous remediation method provided here, and the practice could be used for similar projects.