The changes of wetting and microstructure of loess under unloading from macroscopic and microscopic viewpoints was investigated. The wet subsidence test was conducted on the loess in Tongchuan area, and the wet subsidence coefficients of constant pressure and unloading were measured at different burial depths, and the differences between constant pressure and unloading and wet subsidence coefficients were compared, and the microstructural changes of wet subsided loess were analyzed by combining SEM(scanning electron microscope) and PCAS(particles and cracks analysis system) observations, and the characteristics of changes in microscopic parameters such as pore area percentage, probability entropy and average shape coefficient were obtained at different burial depths and unloading. The results show these as follows. Unloading will effectively increase the initial pressure of wet sink and reduce the occurrence of wet sink, and change the pore area, particle distribution and arrangement of wet sink loess compared with the constant pressure condition; the microstructure is mainly lamellar and honeycomb structure, with the increase of burial depth and unloading amount, the pore space increases from sparse to dense, and the percentage of fine pore space increases; the probability entropy gradually increases, the particle arrangement becomes chaotic and poorly oriented, and the degree of homogenization. There is a strong correlation between the wetting coefficient, burial depth and unloading volume of loess under the unloading effect.