Abstract: This paper adopts cracking experiments and micro experiment observations of compacted clay specimens under the influence of different wetting-drying cycles. It investigates the effects of wetting-drying cycles on clay cracking and pore structure. Moreover it compares the experimental results of Mercury Intrusion Porosimetry(MIP) and Scanning Electron Microscopy(SEM)tests with those of the macro cracking experiments. The experimental results show that the wetting-drying cycles have a great influence on compacted clay cracking. The Cracking Intensity Factor(CIF),representing the degree of compacted clay cracking, increases as moisture contents decrease, and is obviously larger than that before the wetting-drying cycles. As the number of wetting-drying cycles increases, the total volume of the pores, as the median pore diameter, the mean pore diameter, the mean porosity and the intra-aggregate pores increase. But the intra-particle pores, the inter-particle pores and the inter-aggregate pores reduce obviously. The wetting-drying cycles make the large aggregates of the clay gradually transform into small particles and increase the convexity of the soil particles. Besides, it is observed from the analysis of SEM binary image that the porosity increases with the wetting-drying cycles growing. It is plausible to employ Mercury Intrusion Porosimetry(MIP) and Scanning Electron Microscopy(SEM)tests to analyze and explain the clay cracking. The micro pore characteristics derived from the tests are in line with the macro clay cracking law.