By developing a large scale stress controlled tri-axial testing machine, the creep deformation properties of rockfill material under different conditions were studied. From the laboratory test, it can be found that the creep deformation of rockfill has a direct relationship with cell pressure and stress level. Based on creep deformation test of rockfill samples and the monitoring data of built dams, an empirical model for creep deformation analysis of rockfill material is developed, which assumes the creep deformation of rockfill follows a logarithmic attenuation formula. According to the proposed mathematic model, numerical analysis for a concrete faced rockfill dam was conducted. Stress and deformation status of the dam under the long term operation condition is presented. It could be found that the creep deformation of rockfill has significant impacts on the stresses of concrete face slabs.