Abstract: In this paper, the concept model of soil microstructure is established from the viewpoint of soil microstructure system. According to the nonlinear features of soil, 7 fractal dimension parameters to identify structure state of soil are suggested with the help of fractal theory. On the basis of the above results, the changing characteristics of soft soil microstructure are studied during solidation using Xiamen soft soil as example, and a lot of important results are given. For this reason, more knowledge about mechanics features of soft soil is obtained.