Abstract: In the current design of geosynthetic and pile supported (GSP) composite foundation, a pre-assumed soil arch height is always utilized in load sharing calculation, and the contribution of subsoil resistance is weakened in supporting the embankment fill. To improve the above two defects, the soil arching effect and the geomembrane effect are analyzed, and then the quantitative evaluation methods are presented. In the derivation, the pile-soil differential settlements at pile top and toe are considered, and the arch height can be calculated according to the relative pile-soil displacement. Simultaneously, the neutral point is adopted in skin friction analysis, and hence a formula for the load distribution is obtained based on the mobilized shearing stress developing from bottom to top. This method can take good care of the interaction between the embankment fill, pile-reinforced area and lower underlying layer, which can consider the penetration of pile tops, interaction between piles and surrounding soil and penetration of pile ends. According to the continuity condition of stress and displacement, a load effect solution of GSP composite foundation is obtained. The present method is validated to be reasonable by comparing the analytical solutions with the FEM results and the monitoring data, and can be adopted by engineers when it comes to the situation in presence of the bearing stratum at pile tip with certain stiffness.