In the extraction of U(VI) by tri-n-butyl phosphate (TBP) in bis(trifluoromethylsulfonyl)imides (NTf2-) based ionic liquids (ILs), an unexpected high distribution ratio was observed when P6,4,4,4NTf2 was used as the solvent, where P-6,4,4,4(+) is hexyltributylphosphonium. Further research showed that P6,4,4,4NTf2 was able to extract U(VI) in the absence of extractants, and the extraction ability of P6,4,4,4NTf2 was attributed to the combination of the outer-sphere interaction between NTf2- and U(VI) and the intramolecular interaction between NTf2- and P-6,4,4,4(+). The outer-sphere interaction of NTf2- with U(VI) was theoretically explored by DFT calculation. Walden plot were employed to discover the intramolecular interaction in ILs, among which P6,4,4,4NTf2 showed a much stronger intramolecular interaction than other NTf2- based ILs. Stripping of U(VI) from P6,4,4,4NTf2 was also investigated by use of supercritical carbon dioxide (Sc-CO2). This work shed a light on the role of intramolecular interactions in ILs in the extraction of metal ions.