Abstract: The establishment of underground reservoirs in coal mines has addressed the issue of water scarcity in arid-semi-arid ecologically fragile areas in western China. The repeated rise and fall of the water level in the groundwater reservoir has a damaging effect on the semi-coal-rock dam body and the coal-rock gangue dam body. Based on this, axial compression tests of sandstone-coal assemblies with different "dry-saturated" cyclic immersion times under various confining pressures are designed and conducted, and the deterioration law and mechanism of mechanical properties of coal-rock assemblages under cyclic flooding are analyzed. The results show that:(1)the saturated water content of the composite increases with the increase of cyclic immersion times. There is a logarithmic relationship between saturated moisture content and cyclic immersion times. (2)with the increase of cyclic immersion times, the compaction stage of the stress-strain curve increases, the slope of the elastic stage decreases, the peak stress decreases, the peak strain increases, the yield stage becomes more obvious, and the stress drop slows down. (3)with the increase of cyclic immersion times, the compressive strength of the composite decreases gradually, and the compressive strength deteriorates obviously after cyclic immersion 1 to 3 times. The degree of deterioration in the stage of compressive strength is non-uniform. (4)after cyclic immersion 5 times, the cohesion decreases by 70.87%, and the internal friction angle decreases by 60.65%. (5)after cyclic immersion in water for 1 to 3 times, the elastic modulus of the composite decreases by 53.06%, and the deformation modulus decreases by 61.10%. (6)under the action of cyclic immersion, the micro-cracks of the samples gradually develop, the mineral particles gradually change from the original angular polygon to a round shape, the large mineral particles gradually disintegrate into small particles, and the cementation between the particles gradually weakens from a compact and strong structure to a loose and weak structure. (7)under the action of cyclic flooding, water and rock undergo repeated physical, chemical, and mechanical actions, resulting in repeated damage to coal and rock, leading to the deterioration of macroscopic mechanical properties.