Abstract: The separation of strontium is important in the recovery of radioactive resources. Ionic liquids(ILs) based extraction systems of Sr have been greatly expanded, but the separation of Sr and Cs remains a problem. In addition, the problem of radioactive waste affects the application of IL systems in the field of spent fuel reprocessing. In this work, the macroscopic supramolecular assembly(MSA) of strontium at the interface of IL extraction systems and its basic research on the extraction of Sr were reported. The MSA behavior of Sr²⁺ in ionic liquid based extraction systems was studied and the structure of Sr-MSA was analyzed by mass spectrometry, ¹³C NMR, infrared spectroscopy and theoretical calculation. Sr-MSA was formed by using CnOHmimNTf₂ (n=2, 3) as the ILs and CMPO, TODGA as the extractants. The three-step mechanism of MSA process is proposed: complexes formed by Sr²⁺ and CMPO are extracted to IL phase. The complexes and IL assemble into nanoparticles driven by non-covalent interactions such as electrostatic attraction, hydrogen, hydrophobic interaction. The nanoparticles aggregate into mesoscopic assemblies. The mesoscopic assemblies move to the interface and grow further into macroscopic intermediates. The intermediates finally generate into Sr-MSA under the traction from Marangoni effect. A new method for the selective extraction and one-step solidification of Sr²⁺ from aqueous solutions was developed. The Sr-MSA can be taken out with tweezers easily from aqueous solution. The method can still be used in high acidity environment.