Vapor-liquid equilibrium in the NH3-CO2-H2O system in high pressure and high temperature has been studied. The UNIQUAC-Non Random Factor (NRF) model based on the UNIQUAC model was developed for this system to correlate the experimental data that reported by Goppert and Maurer. This system contains molecules and ions species, therefore the equilibrium equations, dissociation equilibrium reaction. mass balance and electroneutrality was solved simultaneously. The UNIQUAC-NRF model has some binary interaction parameters between molecule-molecule, molecule-ion and ion-ion. These parameters were obtained from experimental data in binary and ternary systems. These parameters were determined by an optimization program and then these were correlated in form of temperature. The results show that this model is in good agreement between experimental data and calculation results for binary and ternary systems. (c) 2006 Elsevier B. V. All rights reserved.