The difficulty of seepage problem lies in the fact that the seepage point is underground and can not be directly observed.It is difficult to directly determine whether it is leaked or not,and it is also difficult to determine the specific scope of seepage and evaluate the effect of leak-stoppage measures.In a large-scale dry-construction dig-in basin project,the cofferdam leakage was discovered by monitoring anomalies (excessive displacement rate,large accumulated deformation,bubbles,water burst,etc.) and monitoring data.The seepage scope was found out by comparing the measured water levels in different cofferdam sections with each other and the theoretical water level.The effect of leak-stoppage measures was evaluated as per comparison on the daily horizontal displacement,water level of cofferdam and seepage flow before and after anti-leakage measures were taken.