In our previous work, a new lattice-fluid equation of state (LF-EoS) was developed and successfully applied to normal fluid systems and ionic liquid systems. In this work, this LF-EoS is further extended to describe thermodynamic properties of polymer systems. First, the model parameters for polymers were determined by fitting experimental pVT data of polymers over a wide temperature and pressure range. Then, the LF-EoS was applied for calculating vapor-liquid equilibrium (VLE) of polymer-solvent systems using one adjustable binary parameter k(12). The solubility of gas in polymer can be calculated up to a high pressure. Moreover, a new parameter C-r was introduced to describe the effect of composition of mixtures on chain length parameter r, and several typical liquid-liquid equilibrium behaviors of polymer solutions can be successfully reproduced.