Abstract: The effect of the struture of chelating agent and synergetic agent on theextraction separation of lithium isotopes by Sudan I-neutral ligand synergeticextraction systems were discussed in this paper. In order to obtain higher isotopiceffect, the chelating agent must possess weaker acidity (pK_a>11), strongerintramolecular hydrogen bonding and a greater tendency to from a six-memberedchelating ring. In the synergetic agent, there must be a functional group possessingstrong coordination ability without steric hindrance. The separation effect (α)increased with the increase in the basicity of the coordinating group. The increaseof the number of chelating rings in the extractable complex was of benefit to theenhancement of α. Further discussions are also made on the enrichment directionof extraction systems and the prospects of different systems to be used for isotopeseparation.