Abstract: Fractures are an important influencing factor of strength decay and permeability increase of expansive soils. The fracture research method of closed-curve localization is proposed based on the expansive soil tests during drying and wetting cycles, to further study the influence of fracture on the strength and permeability of expansive soils. The results show that the method not only significantly reduces the relative error of the average width of fracture, but also the line fracture ratio avoids the problem of directly dealing with the interaction of fracture and boundary conditions, making its meaning more reasonable comparing to surface fracture ratio; further enriches the fracture evolution behavior according to the interconversion relationship between fractures of different width classes; further reveals a linear quantitative relationship among fractures to strength and permeability, which in turn simplifies the non-linear relationship of the number cycles of drying and wetting. The research results have important engineering significance for improving the assessment of the safety state of expansive soil slopes.