Abstract: The softening and argillation of weakly cemented sandstone by water are studied with saturation water experiment, QEMSCAN electron microscopy, and acoustic emission test, so as to explore the changes of the physical and mechanical properties as well as the microstructure characteristics of weakly cemented sandstone under the influences of dry and wet conditions which are imposed in cycles.The results show that the macroscopic characteristics of the softening of weakly cemented sandstone with water are divided into four types. The dif-ferences of such characteristics depend on the way how microscopic particles cement with each other and the mi-croscopic parameters relating to the composition and content of the cement. As of the microscopic features of the softening of the weakly cemented sandstone with water, on one hand, the corrosion of the cements decreases gradually during water saturation, and the self-in-flation of the particles generates fine scraps and grains.On the other hand, during water saturation, the secondary porosity within the rock sample increases.With the increase of the number of dry and wet condition cycles, AE event count rate and energy release rate continue to decrease.The reason is that with the increase of the number of dry and wet cycles, the internal skeleton particles and cements within the sandstone are both softened to different extent, and the crack develops slower with smaller scale and less energy released. Therefore, with more cycles of dry and wet conditions, the damage of the sandstone features lower time count rate and energy release rate, while the severity of the damage towards the sandstone sample is also alleviated.