Abstract: The geometrical structure, electronic structure, and vibrational spectra of NpO₂⁺ were studied by means of 5 types including 23 kinds of density functional methods using relativistic effective potential together with double zeta basis sets for Np and 6-311+G（d） for O. Various DFT methods data show that: (1) the BLYP, G96LYP and B1B95 methods cannot be suited for the ion bond length, the other methods including the BHandHLYP and B3LYP are in good agreement with experimental values; (2) the vibrational frequencies calculated by the BLYP, G96LYP and MPWPW91 methods are much lower than plausible values, the others are consistent with reported values, especially the VSXC and B98 values; (3) to the population analysis data, the NBO population data are more intuitive compared with the Mulliken population data, furthermore, the frontier orbitals energy difference obtained by the BHandH and BHandHLYP methods are higher than others’ values.