This　study　for　the　first　time　proposed　a　novel　hydrophobic　eutectic　solvent　(HES)-based　extractant　composed　of　HES　(i.e.,　trioctylamine　(N235)　as　a　hydrogen　bond　acceptor　(HBA)　and　bis(2-ethylhexyl)　phosphate　(D2EHPA)　as　a　hydrogen　bond　donor　(HBD))　coupled　with　tributyl　phosphate　(TBP)　for　Mg2+　extraction　from　salt　lakes　brines.　Under　optimal　conditions,　Mg2+　extraction　efficiency　and　separation　selectivity　of　Li+/Mg2+reached　to　71.02　%　and　30.86,　respectively,　superior　to　reported　literature　values.　A　novel　extraction　mechanism,　the　socalled　＂multi-component　synergistic　ion　association　mechanism＂　was　identified　for　the　first　time　via　spectroscopic　characterization　and　quantum　chemical　(QC)　calculations.　It　was　found　that　Mg2+　is　extracted　from　the　aqueous　phase　to　the　organic　phase　in　the　form　of　Cl--HES-Mg2+-TBP　complex　based　on　the　complex　multi-site　interactions.　This　study　offers　a　new　route　by　means　of　selectively　extracting　Mg2+　resulting　in　simultaneously　preparing　Mg　metals　or　alloys,　reducing　the　difficulty　of　Li+　extraction.