3D dynamic finite element calculation is carried out for a 161 m high geomembrane faced soft rockfill dam on overburden in a strong earthquake area. The dynamic response of the dam is obtained. The horizontal dynamic displacement is relatively more significant. The maximum vertical permanent deformation and deflection of geomembrane occur at the dam crest near the maximum dam cross section. The tensile strain of geomembrane increases significantly at the dig-fill junction and the reverse arc section. The maximum tensile strain of geomembrane is 1.52%, and the safety factor of geomembrane tensile strain is greater than the allowable value. Even subjected to the strong earthquake, the geomembrane slab can effectively coordinate the deformation with the dam body and deep overburden and the dam can be in a safe operation state.