A modified generalized lattice-fluid (MGLF) model was developed to predict and describe phase behaviours of polymer solutions under high pressure condition. To consider the specific interaction between pure components, a new parameter, kappa(11), was introduced into the generalized lattice-fluid (GLF) model. The proposed model was compared with a phase diagram predicted by the GLF model and experimental data for polymer solution systems (polystyrene/diethylether and polystyrene/acetone) showing lower critical solution temperature (LCST) at various pressures. The MGLF model predicted remarkably well the spinodal curve of a given polymer/solvent system.