Some recent studies on predicting impact sensitivity for different classes of energetic crystals based on first-principles band gap were reviewed. It is found that for energetic crystals with similar structure or with similar thermal decomposition mechanism, the smaller the band gap (ΔEg) is, the easier the electron transfers from the valence band to the conduction band, and the more they becomes decomposed and exploded. This band gap criterion is applicable to ionic or molecular crystals, different polymorphs of energetic crystals, energetic crystals at different pressures,and doped energetic crystals.