In　order　to　master　the　properties　of　blast　shock　wave　on　buildings　in　the　explosion　disaster,　a　numerical　model　for　calculating　the　blast　overpressure　in　the　underpass　was　established　by　using　explicit　dynamic　nonlinear　finite　element　software　LS-DYNA;　the　influence　of　the　grid　division　on　the　calculation　result　of　the　blast　overpressure　loading　was　analyzed;　the　regularities　of　blast　overpressure　loading　to　the　target　building　under　different　TNT　equivalent　and　distance　were　obtained.　Based　on　the　numerical　results,　some　principles　in　the　explosion　disaster　prewarning,　design　and　reinforcement　of　a　blast-resistant　building　can　be　applied　in　the　actual　projects.