Abstract: To investigate the structural stability of lunar lava tubes subjected to meteoroid impacts, a two-dimensional numerical model was developed using the Discrete Element Method （DEM）. Dynamic impact scenarios were simulated, where meteoroids with varying impact velocities and incident angles strike lava tubes with different cross-sectional geometries. The parallel bond contact model was employed to characterize the mechanical behavior of lunar basaltic rock at the particle scale. Analyses of crater morphology, stress-time histories, and contact force chain evolution indicate that the influence of cross-sectional shape is relatively minor. The three tube geometries studied exhibit comparable crater profiles and stress distributions, suggesting that the propagation of impact-induced stress waves is only weakly affected by geometric configuration. Impact velocity is identified as the primary factor governing structural damage. When the impact velocity increases to 30 km/s, the crater depth and width increase by 136.11% and 172.47%, respectively, compared to those at an impact velocity of 20 km/s. The associated peak stresses also rise significantly, and extensive breakage of cemented bonds occurs near the tube crown, forming a continuous shear band that substantially increases the risk of structural instability. The incident angle mainly influences the damage pattern: for an oblique impact at 45°, the crater depth decreases by 26.7% relative to that under vertical incidence, and the reduced energy transmission mitigates deep-seated damage. Nevertheless, at high velocities, significant stability hazards persist even for oblique impacts. The numerical results demonstrate that the relative importance of impact parameters to the stability of the lava-tube roof rock mass follows the order: impact velocity > impact angle > cross-sectional geometry. The simulations further reveal the coupled mechanisms of stress-wave propagation and particle-scale damage evolution in granular rock media. This study provides scientific insights into the vulnerability of lunar lava tubes under meteoroid bombardment and offers a theoretical reference for site selection and safety evaluation of future lunar lava-tube habitats.