Adding pour point depressants (PPDs) to lower the cold filter plugging point (CFPP) of oils has been widely used as the most valuable way in the world. To develop the new type of PPDs according to the oils of different kinds, many researchers have tried to study the performance mechanism of PPDs with different methods. In this article, we have carried out this study with density function theory and molecular mechanics calculation methods. From the results of different systems, we have found that: (1) Alkane molecule is non-polar but the methyl groups on the chain ends have higher electronegativity than all the methylene groups. (2) The EVA (copolymer of ethylene and vinyl acetate) molecule is divided into segments by the polar groups, and the segments are composed of carbon chains, while at the joint points of the segments are ester groups. Calculation results show that the non-polar parts of EVA molecule have good affinity to the adjacent alkane molecules. The rigidity of the carbon bonds neighboring to ester groups is enhanced by the introduction of ester groups, which can also help the next segments to get into the next crystal units and accelerate the growth rate of the planes perpendicular to (001) plane. (3) The alkane molecules absorbed on the PPD molecules can be bent, and the bending conformation brings steric hindrance effect to the molecules to deposit on the surface near the PPD molecules. The relatively higher electronegativity of the methyl groups, which are bent out of the crystal units, can also bring more repulsion effect to the alkane molecules to deposit. This helps to restrict the high growing velocity of (001) plane and results in the uniformity growing rate in three dimensions. (4) If we want to get the good performance properties of PPDs, the carbon number should be a little lower than the mean carbon number of the wax crystals. Then the acetate percent of EVA molecules should be around 30% and the concrete value should be determined according to the oils used. (C) 2004 Elsevier Ltd. All rights reserved.