Phase separation dynamic processes in three-liquid-phase system (TLPS), composed of organic oil (P507 extractant), water-soluble polymer (PEG2000), ammonium sulfate, and water, with the change of mass composition Of phase-forming components were investigated. It was found that dynamic separation of three-layered liquid phases in TLPS is in fact a course of dispersive polymer and organic oil droplets aggregated and separated out respectively from continuous salt aqueous bottom phase. Formation rate of organic oil phase was controlled mainly by coalescence rate of dispersed oil droplets; however, the rate-determining process for formation of polymer middle phase may change from drop sedimentation to coalescence or codetermined by both, when mass composition of the TLPS changed along different operation lines. With the formation of organic oil phase, it becomes another continuous phase, from which dispersive polymer droplets separated out and aggregated into a bulk phase gradually. Phase separation equilibrating time of TLPS, t(E), depends on formation rate of the polymer middle phase and its equilibrium volume. A quantitative correlation of phase separation rate of TLPS with its physicochemical properties Was given. The present work promotes further understanding about influence from change in mass composition of phase-forming components in TLPS on three-phase separation dynamic processes.