<p>This study investigates the influence of material heterogeneity on the mechanical behavior and failure mechanisms of fractured rock. A combined laboratory testing and numerical simulation approach was employed to gain comprehensive insights. Numerical models of sandstone were constructed using Weibull random distribution theory, with homogeneity indices (<i>m</i>) ranging from 5 to 40 and preexisting fracture dip angles varying from 0° to 90°. The mesoscopic parameters used in the simulations were calibrated against experimental data. The results reveal that the strength of fractured sandstone is highly dependent on its degree of heterogeneity. As the homogeneity index increases from 5 to 40, the peak stress of specimens with different fracture dip angles increases by 10% to 28.4%. Crack propagation is found to be jointly controlled by heterogeneity and fracture geometry. As heterogeneity increases, the development of bifurcation cracks follows a distinct pattern, initially increasing, then decreasing, and finally increasing again. For fracture dip angles between 0° and 75°, wing cracks typically initiate at the fracture tips and propagate along the direction of the maximum principal stress. However, at a dip angle of 90°, cracks deviate from this trend, bypassing the prefabricated defects and following more complex trajectories. Based on the simulation results, a “stress field-structural plane” cooperative control mechanism is proposed, suggesting that crack propagation is primarily governed by the interaction between fracture orientation and the local heterogeneous stress field. These findings provide a theoretical basis for evaluating the stability of rock masses containing weak structural planes.</p>