Adding pour point depressants (PPD) to lower the Cold Filter Plugging Point (CFPP) of diesel fuels is an effective and economic way of improving the cold flow properties of the oils. EVAP is a new type of PPD and has an excellent effect in lowering the CFPP of most Chinese diesel fuels. To further the development of this PPD product, its performance mechanism was studied using four kinds of diesel fuels, each with a different response. Differential scanning calorimeter and X-ray diffraction methods were selected as the research measures. According to the experimental results, the growth rate paralleling to (001) plane was cumbered and the integrity of the crystal was greatly improved. The results analysis shows that the EVAP molecules have taken effect by co-crystallization. The crystallinity of the diesel fuels is an important factor in determining the responsibility of the oils. (C) 2003 Elsevier Science Ltd. All rights reserved.