Abstract: Dihexadecyl fumarate-styrene copolymer (FOS) was synthesized by solution free radical copolymerization with benzoyl peroxide as the initiator. The monomer dihexadecyl fumarate (DHF) was obtained by direct esterification of fumaric acid and hexadecyl alcohol using paratoluenesulfonic acid as catalyst, hydroquinone as polymerization inhibitor and toluene as solvent. FOS obtained was then evaluated as a cold flow improving agent for diesel fuel. Zhangjiagang 0# diesel and Shengli Haike 5# diesel were used. The structures of monomer and copolymer were characterized by IR and ¹H-NMR and the composition of diesel oils was analyzed by gas phase chromatography. The effects of FOS on the cold filter plugging point (CFPP) and the depression mechanism were then investigated. The results indicated that the copolymer FOS obtained in this work can be used as the cold flow improver for diesel fuel. The CFPP values of Zhangjiagang 0# diesel and Shengli Haike 5# can be depressed by 6℃ and 3℃, respectively, by adding 0.1% FOS in the diesel oils. The sensitivity of FOS as cold flow improver may vary for different diesel products. When mixed with two kinds of commercial cold flow improvers, FOS exhibits excellent performance and good application prospects as the diesel oil additive.