The stress and strain of an actual earth-rockfill dam were calculated based on three-dimensional finite element method, and the stress path during dam construction and impounding were studied. The result was concluded as follows: Every point inside the dam has a stress path of equal stress ratio both in construction stage and during impoundment period. The ratio between major and minor principal stresses increment basically keeps constant, while it varies with construction and impoundment periods, and the magnitude of ratio changes with position and material. The conclusion may provide the basis for the material test of dam and facilitate the study of constitutive model for the analysis on stress deformation of earth-rockfill dam.