A novel terpolymer, MC-MA-MCNR2, derived from tetradecyl methacrylate ( MC), maleic anhydride ( MA), and methacrylamide (MCNR2) was synthesized. The ability of MC-MA-MCNR2 was evaluated as a cold flow improver in diesel fuel, and the interactions of MC-MA-MCNR2 with several kinds of copolymer were studied. To provide a better understanding of the synergistic mechanism, microscopy was used to study the crystal conformation when MC-MA-MCNR2 and EVA(ethylene- vinyl acetate) are mixed into a diesel fuel. The results indicate that using blends of MC-MA-MCNR2 and EVA, one can obtain a satisfactory cold filter plugging point depression. Based on the microscopy experiment, the synergism mechanism was discussed.