A novel Li+ extraction process from low - grade salt lake brine with ultrahigh Mg/Li mass ratio was investigated using TBP - kerosene - FeCl3 system in this work. The effects of various factors (such as TBP concentration, Fe/Li molar ratio and acidity of brine) on Li+ extraction was first studied, and the optimum conditions of single - stage extraction was identified as follows: TBP concertation was 75%, Fe/Li molar ratio was 1.3, and the acidity of brine was 0.01 mol/L. The extraction efficiency of Li+ and separation factor of Li/Mg in single - stage reached 67.9% and 435.5 respectively. The extraction, scrubbing, stripping and regeneration processes were studied respectively to optimize the operation conditions of each section, and a novel reflux scrubbing process was put forward. Then an eleven -stage whole extraction process experiment was carried out at the optimum conditions. The capacity of Li in organic phase reached 2.0 g/L. The extraction efficiency of Li+ reached 87.9%, and stripping liquor containing 28.83 g/L Li+ and 0.617 g/L Mg2+ was obtained. The Mg/Li mass ratio changed from 370 in salt lake brine to 0.02 in the stripping liquor. The aims of separation, purification and enrichment Li+ were achieved concurrently through the novel extraction process without any other additional process.