Water swelling and drying shrinkage due to moisture change is the expansive soil’s characteristic which is similar to the thermal effect of material. Stress is generated by the swell-shrinking deformation constraints and the concept of moisture change stress is put forward. The moisture change stress is adopted to calculate swell-shrinking deformation based on the thermal stress and elasticity theory. A theoretical model which could calculate the moisture change stress resulted from moisture change is established. The mechanism of cracking is the different rates of water loss in different depths which caused the uneven shrinkage deformation. The critical value of moisture change for initial cracking is presented

which is consistent with measured result. The initial depth of expansive soil cracks is put forward by proposed model. The relationship between the depth of initial cracking and soil parameters such as deformation modulus

swell-shrinking characteristics

etc. are discussed in detail.