There is a voluminous literature on the determination of structural and electrical properties of a nanofiltration (NF) membrane and its separation performance. Theories used to characterize a NF membrane usually include: the non-equilibrium thermodynamic model, the pore model, the TMS model, the electrostatic and steric-hindrance pore model, and the semi-emprical model. In the article, we briefly trace the origins or the general ideas of the above-mentioned theories. From there, recent researches on the evaluation of membrane structural and electrical properties are reviewed. We then turn to research on the separation performance of a NF membrane for single component solutions of inorganic electrolytes, neutral organic solutions, and mixture solution of inorganic electrolytes or that of electrolyte and neutral organic solute. Finally, we conclude with suggestions as to the role of models in the contributions to the application of the NF technology in product separation processes.