A method has been developed for the modeling of complex hydrocarbon mixtures which is based on the accurately simulated distillation gas chromatography analysis as well as the extended method of Ruzicka et al for making the model molecules. The method has been used for modeling of the complex mixture of the lube-oil cut SAE 10 in the aromatics extraction process with the solvent N-methylpyrrolidone (NMP) from the Tehran Refinery. To carry out the liquid-liquid equilibria calculations, the van der Waals surface and volume size parameters of the model molecules and NMP as well as their interaction parameters are required which they are calculated by the Bondi＇s group contribution method with the NMP molecule taken as a functional group according to the approach of Rahman et al. Solvent extraction process at two temperatures of 50 and 42 degrees C both at 1 atm have been carried out in a batch mixer-settler and the properties of resultant phases (extract and raffinate) have been determined by the precise measuring systems using the standard methods of ASTM and the well-known Riazi＇s equations. Finally, the results of the equilibrium calculations have been compared with the experimental data and good agreement was found.