In order to study the molecular structure characteristics of 1,1-diamino-2,2-dintroethylene (FOX-7, a novel material with high energy and low sensibility), the absorption spectra of the explosive in the frequency range from 0.2 to 2.3 THz were detected by terahertz time-domain spectroscopy. The terahertz absorption spectra and the characteristic peaks were obtained. The article also simulated absorption spectra of FOX-7 single molecule and molecular crystal within 0.2-2.4 THz region using density functional theory (DFT), which showed that the interaction between molecules played a major role in forming absorption peaks of FOX-7. Besides, the vibrational modes of the characteristic peaks in the experimental absorption spectra were analyzed and identified. The absorption peak at 1.59 THz was mainly due to the swinging vibration of nitro and amido groups, and the peak at 2.12 THz originated from two kinds of vibrations (the swinging, torsion vibration of the nitro and amido groups).