Hydrate-based gas separation is a promising technology for CO2 capture and storage. Hydrate phase equilibrium data are the most basic information for hydrate formation and dissociation. The effects and mechanism of the additive mixture (mole fraction 1%, 2%, 3%, 4% and 5% tetrahydrofuran, THF, with 1000 mg/L sodium dodecyl sulphate, SOS) on the hydrate phase equilibrium (THF+ SOS + CO2 + N-2 + H2O system) were investigated using an isochoric method. The experimental results showed that the presence of THF resulted in a substantial decrease of the hydrate phase equilibrium pressure. The rate of decrease of the hydrate phase equilibrium pressure with THF concentrations slowed down as the THF concentration exceeded a mole fraction of 3%. An improved model with the PR equation of state associated with a modified Huron-Vidal second-order model mixing rule and non-random two liquid model was proposed further to predict hydrate phase equilibrium. The predictions showed an acceptable agreement with the experimental data. When the hydrate phase equilibrium pressure was higher than 2.00 MPa, the absolute average deviations of the predicted results were obviously smaller. (C) 2014 Elsevier B.V. All rights reserved.