Abstract: Abstract: Expansive soil is a kind of multi-fissure clay rich in hydrophilic minerals. Its strong characteristics of water absorption expansion and water loss contraction make it very sensitive to the change of environmental humidity. In the process of rainfall and evaporation under natural conditions, the structure of expansive soil shows softening characteristics after the initiation and development of dilatant cracks. Its strength and deformation resistance gradually decline and easily lead to slope collapse, subgrade settlement and damage of water conservancy facilities. The degradation of soil strength has a negative impact on the agricultural ecological environment. In order to quantitatively study the evolution characteristics of swelling and shrinkage cracks of expansive soil and the law of disturbance to soil mass, so as to analyze the mechanism of the engineering and ecological environment disasters caused by soil strength degradation, drying and wetting cycle-CT tests on Hefei expansive soil are carried out to obtain the CT images of the internal structure of soil mass under different drying-wetting cycles. The gray value of CT image is extracted to study the change rule of gray value with the action of dry and wet circulation and the distribution characteristics along the axial direction of the sample. Based on the texture feature research method of grayscale symbiosis matrix, the feature values of grayscale symbiosis matrix (Angular Second Moment, ASM and Contrast, CON) are extracted from the CT images to analyze the texture change rules of the crack images in the dry-wet cycle disturbance of expansive soil. In addition, the structural strength of natural expansive soil under the action of drying-wetting cycle is studied by triaxial shear test. The results show that the image gray value reduces along the development of cracks gradually. In the early stage of the drying-wetting cycle, the average gray value is distributed in the axial direction of the sample, but it is gradually uniform in the later stage. The discrete coefficient reaches to its maximum value after three drying-wetting cycles, which increase to 106% compared with that before the dry and wet cycle. The angular second moment (ASM) decreases with the increase of the times of drying-wetting cycles. Moreover, its value in the directions of 0° and 90° is higher than that in the directions of 45° and 135° to 9%. Contrast (CON) decreases with the increase of the numbers of drying-wetting cycles. The value in the 0 °and 90° directions is smaller than that in the 45° and 135° directions to 52%. Thus, it is more sensitive to the direction of texture. The expansion and contraction cracks damage the structure of the undisturbed expansive soil. After five drying-wetting cycles, the strength of the two soils decrease by 62% and 46% respectively, and the difference between the strength of undisturbed expansive soil and remold expansive soil also decrease from 347.3 to 21.3 kPa. The curves of the disturbance functions defined by angular second moment, contrast and the strength of the original soil connection structure are highly coincident. The eigenvalue disturbance function can better describe the strength characteristics of expansive soil under the disturbance of the expansion and contraction cracks.