Abstract: According to the characteristics of the soft soil subgrade reinforced by biaxial reinforcement, the interaction mechanism of geogrids, piles and soil under the embankment loads is analyzed. The embankment and the improved area are treated as a whole with continuous displacements and stresses. The horizontal reinforced mattress is modelled as a thin plate, and the deformation is calculated by the thin plate theory. The arching in embankments and the interaction of pile-soil are also considered. A mechanical model of biaxial reinforcement composite foundation under embankment loads is developed, and a finite difference method is presented to solve the value of pile-soil stress ratio. The present method is validated by comparing the analytical solutions with the test results. The results by the proposed method are compared with the calculated results in the references. It shows that the analytical solutions have better agreement with the measured data than the calculated values from the references. The factors which affect pile-soil stress ratio, such as the tensile elastic modulus, differential settlement, clear spacing between piles and the height of embankment, are systematically analyzed. The present method can be applied in engineering practices.