Abstract: For the hardening process of the stabilized soil, a new structural model of stabilized soil was proposed that the structure formation of stabilized soil included soil particle cementing and pore filling. Based on the new structural model, when silt was used for soil sample and cement for hardening agent, the results show that the theoretical calculations of hardening agent contents used for cementing soil particle and filling pore are identical with those derived from experiment in the structure formation of stabilized soil. Some experimental results can be interpreted by the new structural model, such as the relationship between the mechanism of the strength increase and hardening agent contents of the stabilized soils. Through substituting expansive material for the cement contents used for filling pore in the above-mentioned hardening agent and increasing/decreasing the cement content, the role of soil particle cementing and pore filling to the structure formation was validated. And it was proposed that pore filling was critical to the strength increase of the stabilized soil.