Abstract: The quantitative description of crack features, which is the basis of researches on crack of expansive soils, contributes to further investigation on engineering properties of expansive soils. Taking surface cracks of expansive soils as research objects, the crack images under different wetting-drying cycles are captured by digital imaging. The crack features are analyzed by using the optimized and improved methods for crack image processing and crack feature extraction. The results show that the total surface crack ratio of laboratory compacted expansive soils increases with the number of the wetting-drying cycles, and that the effect of wetting-drying cycles is mainly reflected in the second cycle. The number of cracks is the greatest and the total length of cracks is the largest at the preliminary stage of the first wetting-drying cycle, however, the final number and the total length of cracks are closer after the third wetting-drying cycle. The crack width increases with the increase of the wetting-drying cycles, and is mainly reflected in the second cycle. Meanwhile, the development of the main crack is the most obvious in the first wetting-drying cycle, and the width of cracks tends to be uniform in the second and third cycles. Based on rose diagrams of crack orientation, it is found that the cracks develop along the initial orientation until the next wetting-drying cycle. The crack orientation in the first wetting-drying cycle is random, but the orientation has high similarity in the second and third cycles, indicating that the effect of wetting-drying cycles on the crack orientation is also mainly reflected in the second cycle.