Abstract: The integrity and sealing of the landfill cover layer are crucial for its barrier function. Compacted clay is commonly used as a cover material; however, it is prone to shrinkage and cracking under repeated dry-wet cycles, which compromises its effectiveness. Biochar has attracted widespread attention for its potential to improve soil performance, yet the shrinkage and cracking behavior of biochar-clay mixed soil under dry-wet cycles remains poorly understood. Understanding the effect of dry-wet cycles on crack development of cover soil is of paramount importance. Under the conditions of dry-wet cycles, the crack development test was conducted on the compacted samples of biochar-clay mixed soil with different biochar contents. The shrinkage cracking pictures were quantified with image processing and analysis software, CIAS. computed tomography (CT) scanning was carried out to study the influence of dry-wet cycles and biochar content on the evolution mechanism of the pore structure and the development of microscopic fissures in biochar-clay mixed soil. The results show that the shrinkage and cracking rates and average crack width of the biochar-clay mixed soils were always smaller than those of the clays. Specifically, compared with clay, the shrinkage of the mixed soil with 5% and 15% biochar decreased by 6.1% and 12.7%, respectively; the cracking rate decreased by 12.6% and 56.3%, and the average width of the cracks decreased by 5.37% and 47.9%, respectively. The CT scan results show that the number of pores in the clays increased with the increase in periods of dry-wet cycles, resulting in fissures appearing after 6 dry-wet cycles. There were basically no fissures in the mixed soil samples with 15% biochar content. Under the same number of dry-wet cycles, biochar filled the pores within the mixed soil samples, gradually reducing the number of pores. The incorporation of biochar into the conventional clay landfill cover layer can improve its anti-cracking characteristics and enhance the integrity of the cover soil. This study provides a promising approach to improve the barrier function of the landfill cover system.