Abstract: The effects of saline deterioration and aeolian ullage are the important controlling process for the formation and development of undercutting disease at the bottom of earthen sites in arid regions. Among them, the traces of movement and enrichment of salts and the essence of saline deterioration for anti-erosion ability of soil are the two key issues. Through real-time monitoring of the temperature, moisture and permittivity of three typical sites during concentrated rainfall process, it is found that the larger time gradient difference exists between the changes of temperature and moisture content in soils located in foundation and undercutting areas, providing much power and being a transportation medium for salt to migrate and accumulate into undercutting areas by capillary action. Based on the above monitoring results, and by analyzing the particle sizes and conducting wind erosion experiments on remolded samples of site soils which have experienced different stages of wetting-drying cycles and been cured under different salt types and contents, it is shown that the essential reason for deterioration of soil resistance to wind erosion in undercutting areas is the salt enrichment increment caused by the annual concentrated rainfall in the arid areas and coarse-grained soils and the uniform particle sizes caused by wetting-drying cycles.