A qualitative method, based on the model previously proposed for nanofiltration, was developed to analyze mechanisms involved in solute transport through a given nanofiltration membrane. Convection related to solvent flux and diffusion due to concentration gradient effect have to be taken into account to characterize solute transport during nanofiltration. Evolution and distribution of these two mechanisms as a function of transmembrane pressure and solute concentration are illustrated in this work. It was shown that, in most cases, convection plays the most important role, which demonstrates that the membrane used has fine pores.