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Alkaline clayey soil is considered to be a degraded soil, which causes serious issues in engineering and construction projects. The formation and development of desiccation cracks in alkaline clayey soils is a complex process affecting the strength, stability, and permeability of these soils. Therefore, to investigate how soda content can inhibit the development of desiccation cracks in alkaline clayey soils in Ulanhot, Inner Mongolia, China, free desiccation tests were performed to examine the cracks in alkaline clayey soil samples with different soda (Na2CO3) contents in the laboratory. During the cracking process, the changes in water content and the occurrence and evolution of cracks were recorded with a camera. Digital image processing was performed to analyze the structure characteristics of the surface cracks. The results indicated that the characteristics are influenced by the different soda contents. The soda inhibited the development of desiccation cracks in alkaline clayey soils. Three stages were found in the process of desiccation cracking in accordance with the rate of water loss: the residual, normal, and structural shrinkage stages. At <0.4 mol L-1 Na2CO3, the "three straight lines" model could be used to describe the volume shrinkage. However, at >0.4 mol L-1 Na2CO3, the structural shrinkage stage disappeared. Moreover, based on the general soil volume change equation and fractal theory, a model was formulated to quantitatively explain the relationship between the fractal dimension and the volume changes in the soil. The experimental results and equations are important for reducing subgrade deformation and slumps.