We studied terahertz spectra of hexanitrohexaazaisowurtzitane ('varepsilon'-HNIW and 'gamma'-HNIW), a kind of explosive materials, using terahertz time-domain spectroscopy (THz-TDS) in the 0.2-2.5 THz region. The experimental results show that explosive samples with different conformations have different intermolecular or phonon bands. For 'varepsilon'-HNIW, the observed absorption peaks were located at 0.99, 1.32, 1.43, and 2.08 THz; for 'gamma'-HNIW, the absorption peaks were observed at 1.05, 1.52, and 1.90 THz. The frequency dependent refraction index and absorption coefficients of two samples were also extracted.