［Purposes ］ This paper aims to reveal the deterioration mechanism of the mechanical properties and microstructure of the soil on the bank slope of the Three Gorges Reservoir Area under the periodic variation of the reservoir water level and to provide a theoretical basis for the prevention and control of disasters on the bank slope of the reservoir.［Methods］ The soil at different elevations （145 m，155 m，165 m，175 m，and 180 m） along the bank slope of the reservoir was selected for macroscopic mechanical tests and microscopic mineral analysis，and the deterioration areas of the subsidence zone were divided.By taking the soil in the area with the most severe deterioration as the research object，a “dry-saturated ” dry-wet alternating periodic test of different times （1，2，3，5，and 8 times） was designed to simulate the dry -wet alternating environment of water level rise and fall in the reservoir.Finally，a macro -fine-micro multi -scale combined analysis method was adopted.［Findings］ The soil deterioration in the landslide subsidence zone shows significant elevation differentiation.The fractal dimension increases by 3.6%，and the cohesion decreases by 16.7% in the range of ［145，155 ）m，which is an enhanced deterioration area.In the range of ［155，175］m，the fractal dimension decreases by 5.7%，and the cohesion increases by 50%，which belongs to the area of weakened deterioration.There is no deterioration above 175 m.Under the action of dry -wet cycles，the shear strength of the soil at an elevation of 155 m decays by 28.18% within the first five cycles，and the degree of soil erosion is 4.88%.Subsequently，it tends to be stable.Scanning electron microscopy （SEM） and nuclear magnetic resonance （NMR） tests indicate that moisture intrusion leads to an increase in the content of fine particles and an increase in the proportion of large pores.［Conclusions ］ The deterioration of the soil in the subsidence zone is affected by the variation of the reservoir water level.In the early stage of water storage，the scouring action causes the three -stage damage evolution of "fracture initiation，penetration，and disintegration" within the soil，promoting the transformation of the soil from dense to loose and multi -fractured.In the later stage of water storage，the soil at different elevations has different degrees of contact with the reservoir water，resulting in different degrees of water chemical reactions within the soil.The dissolution of minerals in the soil framework and the fragmentation and cementation of adherents，as well as the synergistic effect of mesoscopic pore network reconstruction and particle erosion fragmentation，are the essential causes of soil deterioration.