To study the anti-cracking effect of fiber-reinforced expansive soil under the dry-wet cycles， the dry-wet cycle tests of plain soil and sisal fiber-reinforced expansive soil were carried out， respectively. The surface crack parameters of the sample were extracted by image processing technology， and the effects of sisal fiber content and length， dry-wet cycle times， and sample moisture content on the crack development were analyzed. The results show that： 1） The sisal fiber-reinforced expansive soil has good crack resistance， and the addition of sisal fiber has a great impact on the crack ratio and average crack width of the expansive soil. Compared with the plain soil sample， the crack ratio and average crack width of the optimal reinforced soil sample are about 1/2 less than that of the plain soil sample. 2） When the fiber length is the same， with the increase of the fiber content， the fracture ratio， the total length of the crack， the average width of the crack， and the fractal dimension all decrease first and then increase， and when the fiber content is 0.4%， each parameter value is the smallest. When the fiber content is the same， the fiber length has little influence on the fracture parameters. 3） With the increase of dry-wet cycles， the fracture parameters of both reinforced soil and plain soil samples gradually increase， but the increase of fracture ratio and average width of fiber-reinforced soil is smaller than that of plain soil. From the fifth dry-wet cycle， the growth of fracture parameters slows down. 4） During the single dehumidification process， when the water content of the sample decreases from 20% to 10%， the fracture develops rapidly， and the development of the plain soil fracture is more sensitive to the change in the water content. When the water content is lower than 10%， the fracture ratio of the sample decreases and tends to be stable. Under the same moisture content， sisal fiber-reinforced soil has better crack resistance. 5） The anti-cracking mechanism of sisal fiber-reinforced expansive soil is mainly manifested in two aspects. On the one hand， the addition of sisal fiber increases the permeability coefficient of expansive soil， promotes the uniform distribution of water in the sample， and reduces the difference between expansion and contraction across the sample. On the other hand， the crisscross sisal fibers restrict the shrinkage of macropores between aggregates.