Low confining pressure triaxial compression tests and scanning electron microscopy (SEM) on silty mudstone were carried out under different drying-wetting cycle paths, respectively, in order to analyze the shallow instability mechanism of silty mudstone slopes in the hot and humid regions of southern China. A damage constitutive model for silty mudstone considering the influence of drying-wetting cycle paths was established based on the continuum damage mechanical theory and the modified Drucker-Prager (D-P) strength criterion. Results showed that the stress-strain curves of silty mudstone manifested non-linear characteristics, and could be divided into the compaction stage, elastic stage, plastic yield stage, post-peak failure stage, and residual strength stage. The compaction stage and the plastic yield stage were prolonged, and the peak strength, deformation modulus, cohesion and internal friction angle damage of silty mudstone gradually increased, with the increase in drying-wetting cycle times or drying-wetting cycle amplitudes. The sensitivity of the mechanical parameters of silty mudstone was as follows: deformation modulus>cohesion>internal friction angle>peak strength. The porosity of silty mudstone kept growing gradually due to erosion and dissolution. The failure mode of silty mudstone specimen evolved from cone-splitting failure, mainly in the form of shear failure, to shear failure. The constructed rock damage constitutive model can consider the influence of drying-wetting cycle paths and reflect the deformation characteristics of the full stress-strain curve of the silty mudstone.