Synthesis of a cold flow improver (MAVA-a) for diesel fuel and its effect on solidifying point (SP) and cold filter plugging point (CFPP) of diesel fuels were investigated. The cold flow improver was prepared by using maleic anhydride (MA) and vinyl acetate (VA) as raw materials, toluene as solvent, dibenzoyl peroxide (BPO) as initiator, through alternating polymerization under nitrogen to obtain a binary-polymer and then through aminolysis by using a higher carbon amine as aminating agent at a temperature of 80 °C. A cold flow improver was designed and prepared for No. 0 diesel fuel from Zhang Jia-Gang Petrochemical Company according to the contents of n-paraffin and its carbon number distribution in the No. 0 diesel fuel. It was also used together with two kinds of ethene-vinyl acetate copolymer improvers (EVA) separately. The test result showed that the CFPP of the No. 0 diesel fuel could be lowered by 3–5 °C when the improver MAVA-a was used. The CFPP was lowered by 8 °C when the improver MAVA-a was used together with EVA-2.