Abstract: In order to investigate the mechanical mechanism of dry shrinkage cracking in compacted clay impermeable layer, the experimental study of water content gradient change and dry shrinkage crack evolution law of compacted clay layer was carried out. Meanwhile, the analytical model of compacted clay layer cracking under the action of water content gradient was constructed. The research results showed that the water loss rate of compacted clay layer decreases with depth index during evaporation, and the water content gradient of high liquid limit clay is significantly higher than that of low liquid limit clay. The tensile stress in the surface layer of compacted clay layer increases with the increase of water content gradient. During evaporation, the water content gradient of low liquid-limit compacted clay layer is small, the surface tensile stress is low, and there are fewer fissures; while the results of experimental and theoretical analysis of high-liquid-limit clay are opposite.