To reveal the pressure-transfer characteristics of the granular materials in the Solid Granule Medium Forming process, the stainless steel balls with diameter of 1 mm were selected as medium to conduct the axial compression experiment. The particle compression process was simulated by discrete element method, and then the variation law of the microstructure was analyzed from the perspective of force chain. The results showed that: In the gradual compression process of granule medium, its force chains distribution changes from the initial circular shape to the elliptical shape. As the stress increases, the force chains get denser and denser. In addition, the lateral pressure coefficient changes in power law with the compressive stress and it tends to be constant when the internal force chains structure gets stable.