In the area with a thick permeable stratum，the dry condition construction under the coastal environment can be achieved by combination of earth-rock cofferdam without water-proof curtain and deep-well dewatering technology. In order to study the influence of deep-well dewatering conditions on the stability of cofferdams，this paper analyzes and discusses the seepage distribution and slope stability of high earth-rock cofferdam during the operation of dewatering wells by GeoStudio based on Egypt port of Sokhna Container Terminal Basin 2 Project. It is established that the relationship curve between different target dewatering levels and the minimum safety factor of the overall slope stability，and compare with the stability of the cofferdam under the condition of open drainage of water collection. The results show that：1）The seepage is obviously controlled by the dewatering well in the process of developing towards the land side. As there is no seep point in the toe of the cofferdam，the stability can meet the safety requirements. 2）When the target dewatering level rises，the stability of the cofferdam tends to decrease. 3）When the target dewatering level falls to a certain depth，the phreatic line reaches a certain depth，and the stability of the cofferdam is almost not affected by seepage while the stability coefficient no longer increases. 4）The analysis results can provide a reasonable design approach for similar projects.