This study conducted static compression tests on specimens using an electro-servo pressure testing machine. Based on the moment tensor theory and PFC2D, acoustic emission discrete element analyses under different confining pressures were performed to investigate the effects of filling materials and confining pressure on the strength parameters, strain field evolution, failure modes, and acoustic emission events of the specimens. The results show that the fillers significantly enhance the compressive strength of the specimens. Compared with the FA specimen, the compressive strength increased by an average of 13.7%, 25.2%, and 33.7% under the three filling conditions, respectively. In specimens without fillers, significant stress concentration was observed around the cavities. For specimens with filled cavities, strain localization was primarily concentrated within the filling material during the initial loading stage and gradually evolved into crack propagation along weak paths in the specimen during the later loading stage. Compared with unfilled specimens, the failure patterns of filled specimens changed considerably, while the macroscopic failure patterns under different filling materials were relatively similar. Moderate-magnitude acoustic emission events dominated the coalescence zones, and tensile and shear failure mechanisms commonly acted together on the macroscopic fracture surfaces under the three confining pressures. The relationship between magnitude and frequency exhibited a typical normal distribution, and the b-value showed a positive correlation with increasing confining pressure.