Abstract: Experimental and theoretical investigations on the vibration spectrum of Cyclotrimethylene-trinitramine（RDX）-in the region of 0.2～2.5 terahertz are presented. The refractive index and absorption coefficient of an explosive sample were measured by terahertz time-domain spectroscopy. The theoretical simulation according to density functional theory (DFT) is in agreement with the experimental data. The obtained results indicate that the single chemical compound explosive RDX has a characteristic absorption peak, and the single chemical compound explosive can be tested and identified with THz-TDS technology.