Abstract: The increased water content in the rock will significantly reduce its mechanical properties, potentially leading to geological engineering disasters such as landslides, dangerous rockfalls, dam instability, large tunnel deformation, and underground space instability. Therefore, studying rock mechanical behavior and damage rupture mechanisms under different water content conditions provides a theoretical basis for preventing these disasters. This paper investigated the impact of water content on rocks’ mechanical behavior and microfracture evolution. Experimental results indicate that rock strength decreases exponentially as the water content increases, while peak strain increases exponentially. The evolution of the acoustic emission b-value suggests that internal crack development undergoes a process of “crack closure and particle slippage - microcrack initiation and expansion - microcrack coalescence forming fracture zones - fracture zone nucleation forming macro-fractures”. The water content significantly affects the failure mechanisms of sandstone under uniaxial compression, with changes in water content altering the dominant stress type in each stress region and the precursors to critical failure. As the internal water content increases, the failure mode transitions from tensile-dominated to shear-dominated, with a gradual decrease in locatable acoustic emission events and shifts from concentrated to dispersed distribution of acoustic emission sources.