The intramolecular hydrogen-bonding interactions and properties of a series of nitroamino[1,3,5]triazine-based guanidinium salts were studied by using the dispersion-corrected density functional theory method (DFT-D). Results show that there are evident LP(N or O; LP=lone pair)→σ*(NH) orbital interactions related to O⋅⋅⋅HN or N⋅⋅⋅HN hydrogen bonds. Quantum theory of atoms in molecules (QTAIM) was applied to characterize the intramolecular hydrogen bonds. For the guanidinium salts studied, the intramolecular hydrogen bonds are associated with a seven- or eight-membered pseudo-ring. The guanylurea cation is more helpful for improving the thermal stabilities of the ionic salts than other guanidinium cations. The contributions of different substituents on the triazine ring to the thermal stability increase in the order of NO2<NF2<N3 (ONO2)<NH2. Energy decomposition analysis shows that the salts are stable owing to electrostatic and orbital interactions between the ions, whereas the dispersion energy has very small contributions. Moreover, the salts exhibit relatively high densities in the range of 1.62–1.89 g cm−3. The detonation velocities and pressures lie in the range of 6.49–8.85 km s−1 and 17.79–35.59 GPa, respectively, which makes most of them promising explosives.