Abstract: Lime-treated expansive soil is of cluster structure . The micro-strcuture is made of particles, and the pole is made of micro-pole of inner of particle and the poles between particles , including a part of cementation materials poles. The test results show that the smaller of particle, more helpful for combining of lime and soil. Micro-structure is the chain structure; the quantity of lime mainly effect micro-structure of the surface of soil particle. Ca2+ can immerge to inner of the particle saturation, and there is a similar structure in out layer with its inner layer. The samples with the same quantity of lime, there are different distributions of weight relative contents of Ca for saturated and unsaturated conditions. At the unsaturated condition, the content of Ca2+ is relatively more on the surface and less in the inner. aeat. At the saturated condition, the mount of Ca on the surface is slightly more than that in the inner , and the particles can be larger.