On the basis of the characteristic complicated composition of diesel, a state equation was applied to the description of the liquid phase, and regular solution theory was applied to the description of the solid phase for the sake of calculation of the compositions of the liquid and solid phases in equilibrium. For the first time, the non-n-alkane composition is regarded as a pseudocomponent. The thermodynamic model can successfully predict the solid appearance temperature which is close to the cloud point. The trend of how every n-alkane in diesel was settled is studied by the means of the calculated result of the compositions of the liquid and solid phases. The proportion of heavy n-alkanes in solid is still little, while the deposition trend of heavy n-alkanes is superior to that of light n-alkane because the proportion of heavy n-alkanes in original diesel is small. n-Eicosene, n-octadecane, and n-docosane are the most easily precipitated in diesel. The average carbon number of n-alkanes in settled solid becomes less with an increasing temperature. The phenomena that the settled waxy crystals entrapped significant amounts of liquid can be explained by calculated results which were gained from the thermodynamic model.