The coupling effect of wetting-drying cycles and water content poses a direct threat to the safety of rock slope engineering. This study aims to deeply investigate the degradation patterns of rock mechanical properties. Using synthetic sandstone as the experimental material, uniaxial compression tests were conducted under various cycle numbers (0, 1, 5, 10, and 15) and moisture states (dry, semi-saturated, and saturated). Digital Image Correlation (DIC) technology was employed to achieve full-field tracking of the deformation and failure process of the sandstone. The results indicate that: ① With the increase in cycle numbers, the dry mass (m1) of the sandstone decreases slightly by 0.56%, while the saturated mass (m2) increases significantly by 2.70%, and the growth rate of the saturated water content gradually slows down. ② DIC monitoring reveals that the increase in cycles leads to increasingly severe radial deformation, and the relative growth coefficient of the Poisson's ratio exhibits an exponential growth trend (R2>0.985). ③ Both the relative attenuation coefficients of compressive strength and elastic modulus show a distinct exponential decay trend (R2>0.940) as the number of cycles increases, reflecting significant performance deterioration characteristics. The research results reveal the multi-parameter synergistic degradation mechanism of sandstone under the coupled action of wetting-drying cycles and water content, providing an important reference for the stability analysis and long-term safety assessment of rock slopes.