A local composition model based on the lattice theory, which is a modified non-random two-liquid (NRTL) equation, is developed for the representation of the Helmholtz free energy of polymer solutions. A simple temperature dependence of the model parameters is introduced to account for the oriented interactions without framework for both correlating and predicting the-phase equilibrium of polymer solutions. Special attention is paid to the representation of phase behavior of homologous polymer solutions and systems with or without oriented interactions.