Abstract: The variations law of meso-structure and shear strength of expansive soil under the condition of dryingwetting cycles were studied with CT technology and normal direct shear experiment． Defining damage variable based on CT number，the relationship of the change of the strength parameters and the structure resulted from drying-wetting cycles was established． The results showed that the influence of the 1st to the 4th times of drying-wetting cycles on the structure of expansive soil was bigger，the development of internal fracture was obviously． The influence of the 7th to the 8th times of drying-wetting cycles on the structure was little． After the drying-wetting cycles，the strength attenuation of expansive soil was mainly decrease of cohesion，and the variation of internal friction angle was not significant． With the increase of drying-wetting cycles，the damage variable of the specimens increased gradually，and the evolution of meso-structure damage was a non-linear accumulating process． CT damage variable of expansive soil with its cohesion had a good exponential function decay relationship．