Dry-wet cycle effect is an important factor affecting slope stability in red mudstone reservoir area. Triaxial consolidation undrained shear experiments, CT scans and high precision scanning electron microscopy experiments were carried out to investigate the mechanical and fracture evolution characteristics of in situ weathered mudstones during dry and wet cycles. The results show that the stress-strain relationship of red-bed mudstone presents strain softening characteristics at low confining pressures and strain hardening characteristics at high confining pressures. The shear strength parameters of red-bed mudstone decrease gradually during the dry-wet cycle. The volume content of cracks decreases exponentially with the increase of the time of dry-wet cycles, and has a negative linear correlation with cohesion function. The microstructure of mudstone gradually breaks down in the process of dry-wet cycles, leading to the connectivity of cracks and the attenuation of mechanical properties.