<p>Water is a significant factor inducing deformation and instability in engineering rock masses. Therefore, investigating the micro responses and fracture patterns of rock masses after encountering water based on the field stress distribution is of crucial importance for understanding the damage mechanisms of surrounding rocks. In this study, focusing on the red-bed sandstone formation of the Dali II Section of the Yunnan Dianzhong Diversion Project, experimental research was conducted utilizing devices such as a pressurized water absorption apparatus, a hydro-mechanical triaxial testing machine, nuclear magnetic resonance, and CT scanners. Experimental results indicate that under the same seepage water pressure, the maximum water absorption of samples decreases with increasing confining pressure. By establishing a strength softening function expression based on the peak strength of samples under different water saturation states, the evolution laws of micro-pore structures during strength softening processes were derived from the functional relationships among water saturation, water absorption time, and peak strength values. By comparing the percentage occupation of various scale pore structures under different confining pressures, the rates and proportions of water molecule entry into micropores, mesopores, and macropores of samples under confining and seepage water pressure conditions were obtained. Subsequently, CT scans were conducted on samples subjected to stress loading to quantitatively analyze the evolution patterns of cracks under seepage water pressure and confining pressure effects. Utilizing box-counting theory, the extent of crack propagation in samples was quantitatively characterized.</p>