To provide dry construction conditions for the main project of Xiaoxiang Ship lock,a transverse cofferdam needs to be filled in the upstream to form a main pit construction cofferdam with Songjiazhou on the right bank and Xiaoxiang West Road,which involves seepage and anti-seepage analysis of the combined cofferdams.The connection between the transverse cofferdam upstream and the longitudinal cofferdam on Songjiazhou is susceptible to the impacts of the groundwater seepage caused by the main stream of Xiangjiang River on the north-east side of Songjiazhou.The seepage problem in this project involves mostly saturated-unsaturated soils,and the seepage of water in saturated-unsaturated soils needs to be considered comprehensively.Based on the saturated-unsaturated theory,this paper uses GeoStudio software to model the upstream lateral cofferdam and the combined cofferdam on the right bank of Songjiazhou in three dimensions with regard to the structural form and rock distribution characteristics of the cofferdam of the Xiaoxiang Ship Lock Project.The numerical simulation results are analyzed for seepage and anti-seepage analyses from the perspectives of pore water pressure,water head,and seepage vector.