In a port engineering project，monitoring data reveal the presence of leakage channels under the cut-off wall. Grouting under the wall has been proven highly effective against the leakage.The key technical points are summarized regarding the design and construction for the leakage treatment under the cut-off wall in the project，encompassing the anti-leakage standard，determination of the sealing range，layout of grouting holes，grouting depth，grouting sections，grouting pressure，and grouting technology.Taken together，they form a set of technology for the treatment of leakage under cut-off walls.The sealing range determination based on water level observation breaks through the traditional technology，which can provide a reference for subsequent projects.