In this paper, the content and carbon number distribution of n-alkanes in the three diesel fuels were analyzed by high-temperature gas-phase chromatography. The diesel distillation ranges were determined by a distillation analyzer. Phthalic anhydride-polyethylene glycol ester (PAP) was prepared by using phthalic anhydride and polyethylene glycol (PEG) as the reactant; after that, PAP was reacted with hexadecanol to produce PAPE. The expected products were identified by H-1 NMR spectra. Factors such as the molecular mass of PEG on the wax dispersant for the diesel effect of PAP and PAPE for Yanhua hydrogenation diesel were studied. It is shown that the cold filter plugging point (CFPP) can be depressed 5 and 4 degrees C, respectively. The compositions of wax dispersant and the pour point depressants (PPDs) were investigated. At the same time, the suppressing wax separation test was evaluated, and the effects on reducing the CFPP of diesel oils were studied also. The results showed that the complex of wax dispersant and PPD with vinyl acetate monomer had good synergism. What's more, both PAP and PAPE have the effect on depressing the CFPP for three diesel samples for a certain degree; besides, it had the function of suppressing the wax separation.