Abstract: To evaluate the damage ability of conventional warhead to underground buildings, the fault tree structure, damage levels and damage criterion for the key components of underground buildings were obtained. The damage assessment models of the underground buildings attacked by warheads were established by the Monte Carlo method and degraded state assessment method. The global distributions of the components damage state vector of the underground building under various target-threat interaction initial conditions were gained, and the kill probability of performance degraded state distribution in every function sub-system and the overall vulnerability index for underground command post were given.