The mechanical degradation of fractured rock in water-rich strata critically affects engineering safety. This investigation examines the damage and failure characteristics of water-saturated fractured sandstone through macro-and meso-scale analyses, using Baoshishan Tunnel sandstone. Specimens with a single prefabricated flaw underwent uniaxial compression after varying immersion periods (0 h, 5 h, 15 h). Findings reveal that prolonged immersion increases water content, leading to a marked decline in uniaxial compressive strength and Young’s modulus. Macroscopic failure modes also grow more complex with extended immersion time. Additionally, a particle flow code (PFC3D) model simulated the fracturing process, revealing that meso-damage, predominantly tensile cracking, intensifies with immersion duration, though the fundamental failure mechanism remains unchanged.