Abstract: The deterioration mechanism of rock under wetting and drying cycles is complex. Taking sandstone as the research object, based on the ion concentration in immersion solution, the dissolution of sandstone minerals is quantitatively analyzed, and the evolution laws of sandstone porosity are obtained. Finally, the deterioration mechanism of sandstone under the effect of wetting and drying cycles is analyzed. The results show that the formation rate of Ca²⁺ is one order higher than that of K⁺, Na⁺ and SiO₂, and the formation rate of Fe²⁺ is the lowest. After each cycle phase, the volume reduction of calcite is the most, followed by that of potash feldspar and soda feldspar, while the volume reduction of black mica and quartz is the smallest. After wetting and drying cycles, the micro porosity changes, which will lead to a significant reduction in compressive strength, and the porosity change rate is positively correlated with the deterioration degree in each stage. After erosion of wetting and drying cycles, various minerals are dissolved in sandstone, leading to the decrease of cements and the increase of porosity, producing a variety of voids and micro cracks, and ultimately reflected in the decrease of the strength, which is the main cause of deterioration of sandstone after wetting and drying cycles.