The invention relates to a method for separating rare earth ions by extraction of a liquid-liquid-liquid three-phase system, and belongs to the technical field of rare earth extraction and separation. The method comprises the following steps of: adding a chemical complexing agent into an aqueous solution containing the rare earth ions, regulating the acidity of the solution, adding a water-soluble high polymer and an inorganic electrolyte salt, oscillating and mixing at room temperature, and obtaining a liquid phase system of upper and lower layers; adding a hydrophobic ionic liquid, fully mixing the solution at room temperature, and obtaining an insoluble three-liquid phase coexistence system of upper, middle and lower layers; and respectively taking the upper, middle and lower phases ofthe three-liquid phase system, and reclaiming the rare earth ions by using an electro-deposition method. According to the method, a volatile organic solvent is not used, so that the phase forming behavior and the phase separation process of the three-phase system are easily artificially controlled; and light, medium and heavy rare earth ions are selectively enriched or grouped and separated in three different liquid phases respectively. Compared with conventional oil-water two-phase separation, the method has the advantages that: the process flow is greatly simplified, the method is quick in phase separation and avoids emulsifying, and the hydrophilic and hydrophobic properties of the ionic liquid three-phase system are easily controlled.