The finite element geometric modeling methods commonly used for the geosynthetic reinforced and pile-supported embankments include the single pile model (including axisymmetric model and single pile three-dimensional (3D) model), the plane strain model and the full 3D piled embankments model. These models have different characteristics and assumptions, however, few studies have been carried out to focus on the comparison. The geometric modeling analysis is carried out by using the nonlinear finite element software ABAQUS combined with the field testing results. The differences and causes of stress distribution and deformation between the models with hypothesis of large-area surcharge filling and the full 3D piled embankments model with slope are compared and analyzed. The results of numerical model calculation show that the full 3D piled embankments model can best fit the real performance, while both the single pile model and the large-area surcharged full 3D piled embankments model underestimate the settlement. Due to the horizontal displacement and uplift swelling caused by embankment slope, the settlement difference, average stress ratio between pile and soil, the load sharing coefficient of the pile and lateral tensile stress of the geogrid all reach the maximum values under the shoulder region of the embankment. Meanwhile, under the pavement area, all the four parameters of the full 3D model with slope are larger than those of the full 3D piled embankments model with large-area surcharge filling. The numerical simulation results given by this paper can provide a meaningful reference for the geometrical numerical modelling of composite foundation under embankments and the analysis of the three-dimensional slope effect of embankments.