Abstract: Soil shrinkage cracking is one of the key factors affecting the mechanical strength and hydrological behavior of soils. However, the influence of soil thickness on the drying and cracking process of laterite remains poorly understood. This study used granite laterite as the research object and applied digital image processing to quantitatively analyze crack evolution characteristics, focusing on the effect of soil thickness on the dynamic development of desiccation cracks. The results show that as soil thickness decreases, the evaporation rate increases and the time required for complete evaporation is reduced. Thicker soils exhibit a longer critical time before the first crack appears and a higher critical moisture content. When soil thickness increased from 5 mm to 30 mm, the critical moisture content for cracking increased by 7.56%. Sample thickness significantly influences the shrinkage cracking process: thinner samples develop denser crack networks, while thicker samples show a distinct boundary effect. Compared to the 5 mm-thick sample, the 30 mm-thick sample exhibited a 47.25% higher crack ratio and a 388.88% increase in average crack width, while the number of cracks was only about 1/12 of that in the thinner sample. The equilibrium moisture content at which cracking stabilizes is negatively correlated with soil thickness: increasing thickness from 5 mm to 30 mm reduced the equilibrium moisture content by 7.29%. Cracking results from the combined action of tensile strength, basal adhesion, and tensile stress. Because basal adhesion transmission is influenced by thickness, thicker soil layers experience lower basal restraint on the evaporating surface, leading to higher cracking moisture content. In summary, increasing soil layer thickness suppresses crack development and significantly simplifies the crack network. These findings enhance the understanding of thickness effects on cracking in red-soil hilly regions and provide fundamental support for elucidating the mechanisms of crack development.