The extraction of Li+ from the high Mg/Li ratio brine was performed using hydroxyl functional ionic liq-uids(ILs)as the coextractant and tributyl phosphate(TBP)as the extractant.Firstly,the extractive system,1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide([HOEmim][NTf2])+ TBP was proved to exhibit the highest extraction efficiency of Li+(88.15％)from LiCI aqueous solu-tions among the extractants composed of different ILs,TBP,and ILs + TBP.Effects of various extraction parameters on the extraction efficiencies of Li+ and Mg2+ were then investigated.95.01％ of Li+ was extracted and the Li/Mg separation factor reached 405.76 in a single-stage at 278.15 K and O/A of 2:1.The extraction complexes were determined by the slope analysis method and ESI-MS analysis,and the metal complexes in the organic phase were indi-cated to be mainly[Li.2TBP][NTf2].The striping study showed that 92.86％ of Li+ was stripped with 1.0 mol·L-1 HCI.98％ extraction capacity of the synergy extractants was remained after 5 regeneration cycles.The thermodynamic parameters(AG°,AH°,and AS°),together with the mechanism of the Li+ ex-traction were further demonstrated finally.According to the results,[HOEmim][NTf2]+ TBP extraction system showed promising performance in extract-ing lithium from salt lake brine with high Mg/Li ratio.