In order to study the damage capability of high power microwave bomb (HPMB) attacking target vertically, based on its damage range power circle, and combined with the energy threshold of HPM damage and interference electronic components, the concepts of failure zone, interference area and safe area of damage area were proposed, and the damage zone model which could reflect the damage effect of HPMB was established. Finally the damage capability of HPMB was quantitatively described by a specific example; and the situation of damage area in power circle while HPMB detonating at different heights was obtained. The research process and conclusions offered theoretical basis for setting the attack parameters of HPMB.