Mine pillars are in-situ rock left after mining to ensure mine safety. The determination of pillar sizes dictates the cost of mining and mine safety. In this study, the rock fracturing progress analysis program, RFPA, was adopted to simulate pillars of various sizes to understand their failure mechanisms and patterns. The simulation results indicate that with increasing pillar size, the failure mode changes from tensile splitting to shear failure of the pillar with failure initiating from the pillar boundaries. Failure first occurs on the pillar surface and gradually develops toward the core of the pillar. Finally, shear failure occurs in the pillar. With increasing dip angle of the pillar, stress concentration first appears at the four corners, leading to micro-cracking. As the stress in the pillar continuously increases, micro-cracks gradually coalesce. Subsequently, spalling occurs and failure ensures at the pillar core.