Two kinds of phase transitions (α→β and β→γ) of the insensitive high explosive, 1, 1-diamino-2, 2-dinitroethylene(FOX-7), have been investigated by temperature-dependent Fourier transform infrared(FTIR) spectroscopy, and the effects of intermolecular H-bonding interactions and molecular structure in the phase transitions of FOX-7 were discussed. The frequency of ν₁₁ [NH₂ (ν_as)] and ν₁₀ [NO₂ (ν_s)] shifts about 20 cm^-1, together with the loss of ν₁₈ [C—NO₂ (ν)] in the range of 55 ℃ to 122 ℃, while ν₁₂ [C—NH₂(ν)] disappears and ν₂₀[NO₂(ω)] transforms to another broad peaks in the range of 122 ℃ to 190 ℃. The analytical results of the IR spectra indicate that intermolecular hydrogen bonding interactions change in the phase transitions of the FOX-7, which cause the changes of the molecular structure. Moreover, in the process of α→β transition, the changes of H-bonding length with increasing temperature are not consistent with the linear thermal expansion formula, and ν₁₁、ν₄[Fermi resonance between the NH₂ (ν_as) and the overtone mode of the NH₂ scissor (2ν₅)]、ν₇ and ν₁₀[NO₂(ν_as)] show special frequencies, which are different from those of α and β-FOX-7. The results confirm the transition state in the α→β transition.