<p>Dynamic compression properties and fragmentation characteristics of water-bearing rocks were crucial for the effective excavation of tunnels and mining engineering in groundwater environments. To investigate the dynamic mechanical properties and fragmentation characteristics of rock with different water contents, a series of static and dynamic compression tests were conducted on sandstone. The experimental results show that the dynamic strength of sandstone decreases with increasing water content but increases at higher strain rate. Furthermore, compared to dry sandstone, the dynamic increase factor (DIF) of saturated sandstone is higher, implying that pore water amplifies the strengthening effect of strain rate on dynamic strength. Quantitative analysis of fragment size distribution using standard sieve methods revealed that higher water content and strain rate lead to smaller average fragment sizes and increased degree of fragmentation. Based on the fragment size distribution data, a modified fragmentation prediction model was developed, incorporating both strain rate and pore water. The proposed model shows good agreement with the experimental data and resolves the underestimation of the transition strain rate reported in prior studies. The model indicates that the reduction in surface energy density caused by water may contribute to the smaller fragment sizes observed in water-bearing specimens.</p>