Abstract: The wetting-drying and freeze-thaw(WDFT) coupling effect is an important factor leading to the deterioration of the expansive soil foundation in the cold regions, and the direction of fissure development in the expansive soil foundation has a profound impact on the long-term safety and stability. Focusing on the directionality of crack development in expansive soils, a unit test of the characteristics of surface crack development under WDFT coupling boundary conditions is carried out using the self-designed unidirectional environmental boundary loading device, and the digital image acquisition and processing methods are used to obtain characteristics of surface fissure development under WDFT coupling cycle. The test results show that the liquid water content in the expansive soil during freezing has an important effect on the distribution and morphology of surface cracks. When the critical saturation is large, the freezing process promotes the cracks, and vice versa. The fracture rate gradually stabilizes at later stage of WDFT. Based on the gray histogram of the fissure image, the local directionality of fissure development is calculated by the gradient direction method, and the dimensionless influence factor is introduced to quantify and summarize the fissure angle. The crack evolution laws of expansive soil are further investigated. The quantitative analysis method used can provide reference for related researches.