Density functional theory calculations were performed on crystalline dihydroxylammonium 5,5’-bis(tetrazole)-1,1’-diolate (HATO) under high pressure up to 40 GPa. The GGA-PW91 method in combination with the ultrasoft pseudopotentials reproduced the experimental crystal structure of HATO and was thus employed for the optimizations of both molecular structure and cell parameters. The intermolecular O…H distances generally decrease with increasing pressures. However, the O—H and N—H bond lengths change irregularly upon pressure. Based on the optimized crystal structures at different pressures, the non-periodic calculations of frequencies with a scaling factor of 0967 9 were used to predict both the IR and Raman spectra. The predicted strongest Raman peak at 1 580 cm-1, involving C—C stretching and NH2 symmetric deformation, is in agreement with the experiment. Although there is no hydrogen atom in the anion moiety of HATO, the deuteration in cation still affects the vibrational mode of anion. For O—H and O—D vibration modes, the Raman shifts decrease due to the strengthening intermolecular hydrogen bond as the pressure increases. Upon deuteration, the most characterized change of Raman shifts for ND2 is that the ν2 stretching mode increases dramatically with high pressure as compared to those of NH2, which leads to a coupling of ND2 ν2/ν3 modes at high pressure. The calculated isotopic ratios, ν(NH2)/ν(ND2) for ν1 to ν3 modes, are in the range of 136～138, which are in consistent with the value from the reduced masses of these atoms. The couplings of vibrational modes change with both deuteration and pressure.