Abstract: The interaction and pressure gradient equation of fluid-solid was defined on the basis of particle flow theory using FISH language embedded in PFC2D,and the continuity equation and N-S equation for fluid-solid two-phase flow model in incompressible fluid were solved.It attempts to get insight into the changes in the mechanical properties of soil subjected to seepage erosion under various pressure differences.The variations of fluid velocity,permeability,porosity and the percentage of eroded particles,etc.were obtained qualitatively in the test.The simulated results were consistent with the experimental results,and the obtained fluid velocity and hydraulic gradient satisfied the Daycy’s law.So it was of practical and theoretical significance to simulate the complex interaction between the fluid and soil,and it provided the theoretical basis for the further study of more complicated seepage failure problems in porous media such as flowing soil,piping,etc.