<p>The mechanical properties of rock specimens are significantly influenced by the aperture of pre-existing crack; however, the mechanisms governing this influence remain unclear. In this study, uniaxial compression tests were performed on sandstone and granite specimens containing pre-existing cracks with apertures of 0.2 ~ 1.5&#xa0;mm at inclination angles of 45° and 60°. Acoustic emission (AE) and digital image correlation (DIC) techniques were employed to monitor the damage process and analyze the cracking evolution of the flawed specimens. The results revealed that uniaxial compressive strength and deformation modulus tend to decrease with increasing aperture if the pre-existing crack remains open during compression. The influence of aperture differs between granite and sandstone. Compared with granite, sandstone specimens exhibit a more pronounced and longer-duration post-peak stage. Moreover, the proportion of post-peak AE energy to total AE energy in sandstone specimens gradually increases with increasing aperture. Crack aperture affects the crack propagation process of specimens at both the microscale and macroscale. As the aperture increases, the new wing crack exhibits a larger initiation angle with the pre-existing crack, and the distance between the pre-existing crack tip and the new crack decreases. Rock specimens containing pre-existing cracks with larger apertures tend to develop longer cracks with a higher proportion of shear cracks. AE moment tensor inversion results further demonstrate that the proportion of shear-type sources increases with growing pre-existing fracture aperture. Crack initiation mechanism revealed by AE moment tensor inversion and DIC indicate that far-field cracks are mainly tensile cracks, and their initiation and propagation are closely related to the ultimate specimen failure. These new findings provide important insights into the failure mechanism and prediction of fractured rock, aiding in the monitoring and stability analysis of rock masses.</p>