Aqueous two-phase systems (ATPS) have the advantages of environmentally friendly, high mass transfer efficiency, mild extraction conditions. However, it is difficult to recycle these components, which limits the large-scale application of ATPS in industrial production. In this study, a novel recyclable ATPS of PN/PADB4.78 was constructed with a thermo-responsive polymer PN and a pH-responsive polymer PADB4.78 for the partition study of tea saponin. The recovery of PN reached 98.71% by adjusting the temperature to above its lower critical solution temperature (LCST, 33.0 °C ) and the recovery of PADB4.78 was 97.32% by regulating the pH to its isoelectric point (pI, 4.78). Meanwhile, the phase formation mechanism of ATPS was studied by surface tension and low-field nuclear magnetic resonance (LF-NMR). The effects of polymer concentration, pH, temperature, types and concentrations of salt were investigated on tea saponin partition. In the 1.5% PN/3.5% PADB4.78 ATPS, the optimal partition coefficient (K) and extraction recovery (ERb) of crude tea saponin were 0.15 and 92.13% in the presence of 1.5 mM KCl at pH=7.6 and 25℃, respectively. The K and ERb of tea saponin from tea seeds were 0.12 and 94.50% with 7.5 mM LiBr at pH=8.0 and 25℃, respectively.