To improve the laying and connection type of composite geomembrane and to enhance its adaptability to cofferdam deformation is the key to the design of earth-rock cofferdam with composite geomembrane as seepage control system. Centrifugal model test was carried out to obtain the strain distribution of geomembrane in water-storage period; numerical simulation of the centrifugal model test was also conducted by using the membrane unit M3D4 provided by ABAQUS to acquire the spatial distribution characteristics of stress and deformation of composite geomembrane with different laying and connection patterns. The numerical simulation results were compared with the centrifugal model test results, and the comparison illustrated that the stress of geomembrane laid in an S-shape was more reasonable than that in linear type as the S-shape plays a reinforcing role and reduces the settlement of cofferdam. Strain concentrated in the connection part of geomembrane and the restraint effect of flexible connection is between that of anchorage connection and unconstrained connection, implying stronger deformation compatibility. The results of centrifugal model test can be well reflected by the geomembrane simulation algorithm.