In order to study the effect of large span primary fissures on the strength of expansive soil, the statistical work of primary fissures was carried out with Nanyang expansive soil as the object of study. The fractures were generated by computer inversion. The effects of large-span primary fissures on the strength properties of expansive soils were studied by means of multi-scale stiffness parameters calculation of fractured expansive soils. The results show that the ability of resisting deformation is declining with the gradual introduction of expansive soil cohesion and internal friction angle.