To investigate the influence of fissure inclination on the mechanical properties and energy evolution mechanisms of rock during failure, the Particle Flow Code (PFC) was employed to establish sandstone specimens containing prefabricated fissures with different inclination angles. The mechanical behavior of these specimens under uniaxial compression was simulated, and the corresponding influence mechanisms of fissure orientation on rock mass response were analyzed. The results indicate that the peak stress of the specimens gradually increases with increasing fissure inclination angle, whereas the peak strain first decreases and then increases, exhibiting a distinct V-shaped variation trend. During the loading process, the total number of cracks generally increases with fissure inclination, while the orientation distribution of cracks shifts correspondingly, reflecting the transition of failure modes under different fissure angles. The internal contact force network is closely associated with crack evolution, with fracture initiation occurring preferentially in regions of concentrated contact forces. As loading progresses, the contact force chains gradually weaken and eventually lose their load-bearing capacity. Acoustic emission (AE) activity of specimens with different fissure inclinations can be divided into three stages: a quiet stage, an active stage, and an intense stage. After the stress reaches its peak value, AE activity increases significantly, accompanied by rapid crack propagation and a sharp rise in AE events, indicating that AE characteristics can serve as an effective precursor for failure warning. With increasing fissure inclination, both the total absorbed energy and the elastic strain energy at peak stress showed an increasing trend. This study reveals the controlling mechanisms of fissure inclination on rock failure patterns and strength evolution from the perspectives of crack propagation, contact force reconstruction, and energy partitioning. The findings provide a theoretical basis for failure prediction and stability assessment of jointed rock masses.