Four methods of calculating Flory-Huggins interaction parameters from solubility parameters were examined by comparing calculated binodal curves with experimental data. This is a promising method to calculate interaction parameters from solubility parameters because of the wide use of solubility parameters. The fitting results were satisfactory after the optimization of the correction constant according to the membrane casting systems mentioned. The optimized correction constants were 0.09 and 1.01 for the polymer/solvent and polymer/nonsolvent, respectively. The constants were obtained from PES/solvent and PSF/solvent systems and checked with PSF/DMAc/nonsolvent systems. Calculation was carried out, based on Flory-Huggins solution theory, to analyze the behavior of the polymer/solvent/nonsolvent system phase diagram with the influence of parameter sets in a wide range. It was found that with the increment of solvent/polymer interaction parameters or nonsolvent/polymer interaction parameters the miscibility gaps decreased. However, the miscibility gaps increased with the increment of nonsolvent/solvent interaction parameters.