Understanding the structural, geometrical and chemical changes that occur after electronic excitation is essential to unraveling the inherent mechanism of nitro explosives. In this work, relaxed structures of typical nitro explosives in the excited state are investigated by time-dependent density functional theory. During the excitation process, nitro group becomes activated and then relaxes, leading to a relaxed structure. All five nitro explosives exhibit a similar behavior, and impact sensitivity is related to excitation energy of relaxed structure. High sensitivity d-HMX has a lower excitation energy for relaxed structure than b-HMX. This work offers a novel insight into energetic material.