<p>The geometric characteristics of nonpersistent structural planes determine the bearing capacity and stability of rock bridges. To deepen the understanding of cracking behaviors, fracture mechanisms, and instability prediction of fractured rocks, we conducted acoustic–optical compression experiments on red sandstone with nonpersistent flaws of various inclinations. The real-time fracture signals and surface strain field evolution were recorded using acoustic emission (AE) and digital image correlation (DIC) methods, respectively. The findings show that the flaw inclination angle substantially affects the mechanical parameters, cracking behavior, crack propagation, and fracture failure modes. With increasing flaw inclination angles, the strength, elastic modulus, peak strain, and brittle failure characteristics increase to varying degrees. The distribution of dominant macroscopic fracture surface transitions from traversing to bypassing the rock bridges, while the fracture mechanism shifts from tensile to oblique shear failure mode, predominantly attributed to the locking effect of rock bridges. Wing cracks consistently initiate at the tip of the lower prefabricated flaw and arrest at either the upper flaw tip or top surface of the specimens. A large–small–large characteristic rupture pattern described by AE energy rate during unstable crack growth stage can serve as an identifiable precursor to rock instability. Energy magnitude differences Δ<i>M</i> &lt; 0.5 between the rupture events at the peak strength and crack damage stress values can be used as a quantitative constraint criterion for determining rock bridge fracture. Overall, this study lays a physical foundation for reliable instability prediction of rock slopes dominated by rock bridges.</p>