Abstract: The back analysis of the nonlinear Duncan E-B model parameters is carried out based on the prototype observation data of Bashan concrete face rockfill dam during the filling and operation periods. The observed data are employed to validate the rationality of the parameters. According to the back analysis parameters, three-dimensional viscoelastic finite element simulation is performed to calculate the stress and deformation of faceslab during the period from the filling of the dam to the end of flood 7.10. The deformation of connecting panel seam, the separation between concrete slab and cushion layer and the insufficient cushion materials are calcutated. The causes for the third-stage concrete face cracks and locally compressive damage are analyzed. Analysis shows that the settlement of rockfill placement does not converge, and the initial storage is too fast. They are the main reasons for the cracks and the damage. After the flood, there is no major tensile stress area in the dam. The deformation of vertical and peripheral joints is small, and the three-phase panel at the top has a slight separation between concrete slab and cushion layer. The broken line of concrete face is satisfactorily coordinated with the surrounding deformation, and there is no abrupt stress or deformation. The connecting plate to improve the deformation and stress state of the concrete face is effective.