Abstract: Based on the discrete element method (DEM), this study investigates the evolution of mechanical stability in granular materials during shearing within the framework of the second-order work theory. Using meso-loop structures as the fundamental analysis units, a meso-scale second-order work index is developed to reveal the stability, to reveal the distinct stability characteristics inside and outside the shear band, as well as the contribution of different loop types to both local and global stability. The results show that the negative value of the macroscopic second-order work of the dense specimen appears at the peak stress state with the initial formation of shear band, making a bifurcation from a stable to an unstable state. As shearing progress, the instability of loop elements intensifies significantly, leading to the spatial concentration of localized failure. In contrast, the region outside the shear band retains a high level of overall stability. The vanishing pattern of second-order work within the shear band is highly consistent with that of the whole specimen, indicating that the global instability is predominantly governed by local instability within the shear band. Moreover, distinct differences in stability are observed among loop types: 3-cycle loops exhibit higher stability, while 4-cycle, 5-cycle, and especially high-order 6+-cycle loops are more prone to instability. The synchronized destabilization development of these higher-order loops can further amplify local instabilities within the shear band, ultimately triggering global structural failure.