AVS Diesel Fuel pour point depressant, n-alkyl acrylate-vinyl acetate-styrene terpolymers with different alkyl chain length，named as AVS-12, AVS-14, AVS-16 and AVS-18 according to alkyl chain length, were synthesized by radical polymerization, and the effect of the systems on the solidifying point (SP) and cold filter plugging point (CFPP) of diesel fuel was determined. The content and the carbon number distribution of n-alkanes in diesel fuel were analyzed by gas chromatograph; the rheological behavior and crystallization behavior of diesel fuel treated with and without additives were studied using an advanced rheometer and an optical microscope. The results demonstrated that the terpolymer whose alkyl chain length was close to the average carbon number of n-alkanes in diesel fuel had the best effect on reducing the SP and could reduce the SP by 12℃. The terpolymer which made the wax crystals more dispersed and evenly had the best effect on reducing the CFPP could reduce the CFPP by 4℃. The size, shape and aggregation of wax crystals directly affected the CFPP of diesel fuel, while the formation of three-dimensional network played a decisive role on the SP, thus a good diesel pour point depressant should be adverse to the formation of three-dimensional network and detrimental to the formation of too large wax crystals or wax crystals tending to form large clusters.