Abstract: Expansive soil is prone to develop a large number of cracks, which have a significant impact on its engineering properties. A prefabricated crack method of expansive soil samples is introduced to carry out the unconfined compression strength on the expansive soil samples under the specific crack morphology. The influence of the crack morphology on the strength characteristics of the expansive soil is examined, and the mechanism of crack action is revealed. The results show that: (1) The crack morphology has a significant effect on the failure mode of the samples. When the cracks become wider, which are perpendicular to the stress direction, the failure mode changes from shear-tensile failure to tensile failure. When the cracks parallel to the stress direction become more and more, the failure mode changes from shear failure to swelling failure. (2) The shape of the cracks perpendicular to the stress direction has a significant effect on the stress-strain relationship of the expansive soil samples. The wider the crack is, the greater the closed strain is. The deeper the crack is, the smaller the initial crack initiation stress is and the greater the strength increment is. The shape of cracks parallel to the stress direction has no obvious effect on the stress-strain relationship. Based on the results, four types of curves are divided, namely, the multi-level rise, fluctuation rise, multi-level decline and standard curve. (3) The direction of crack obviously affects the strength reduction of the cracked soil. The peak strength of the sample containing cracks parallel to the stress direction is close to that of the non-cracked sample. The peak strength and deformation modulus of the sample containing cracks perpendicular to the stress direction decrease with the increasing crack number, and have a good logarithmic function relationship. The peak strain is less affected by crack. This study can provide a theoretical basis for the shallow instability mechanism of the expansive soil slope, and a guidance for the design and construction of the corresponding cracked soil engineering.