The recyclable aqueous two-phase systems formed by thermo-sensitive polymer (PNB) and pH-sensitive polymer (PADS) have been prepared by our laboratory. In this study, the Flory-Huggins model derived from the lattice theories and the COVE model based on the McMillan-Mayer solution theory were used for correlations and predictions of phase diagrams. The interaction parameters between the solvent and the polymers of the Flory-Huggins model were calculated from solubility parameters. The interaction parameters between the polymers and the COVE coefficients were determined by fitting experimental data. Simulation of Flory-Huggins model and COVE model indicates that the deviation between prediction values and experimental data is less than 0.50%. The COVE model was more effective than the Flory-Huggins model to this system. (C) 2010 Elsevier B.V. All rights reserved.