The energy transfer rates of ammonium nitrate (AN) have been studied. Line widths of Raman spectra of AN were measured as a function of temperature ranging from 3.6 to 180.0 K. The analysis of the experimental line shapes by deconvolution procedure allows to extracting a constant inhomogeneous contribution to the line broadening, due to probably crystal defects, over all the temperature range. On the basis of temperature dependence of the Raman line width of pure Lorentzian contributions, it was confirmed that the dominant mechanism for the relaxation processes of most modes were three - phonon and dephasing processes. A contribution of three - phonon down population relaxation to the line width could be sparated from the contribution of dephasing processes by extrapolating the Raman line width to T = 0.0 K. The energy transfer rates were evaluated in terms of density of vibrational states, which were calculated using General Utility Lattice Program (GULP) codes at the pressure ranging from 0.0 to 20.0 GPa. The sum of energy transfer rates were calculated in the region ω ≤ 702 cm-1 of the phases (V), (III) and (II). The results indicated that the energy transfer rates of the phases (V),(III) and (II) has a maximum value at 7.0, 11.0, and 11.0 GPa, respectively. The maximum energy transfer rates of the phases (V), (III) and (II) are 2.9, 3.6 and 11.1 times of the value at an ambient pressure, respectively.