Abstract: Taking Linyuan crude oil of Daqing oilfield and the diluted 0# diesel as the research object，the rheological behavior，freezing point，static yield stress and wax precipitation process of the crude oil diluted with 10%，20% and 50% diesel at 65℃ and / or 50℃ are measured and analyzed by using a HAAKE RS600 Rheometer and XP-300C Image Analysis System，and the dynamic viscosity-temperature characteristics at 15s^-1 during the temperature dropping and the wax crystal microstructure at the final testing temperature of 20℃ are also evaluated.The numbers and symmetry of wax crystal particles are analyzed by using Ncmivnt software.A method for the symmetry of the crystal particles characterized by the ratio of the average of their short-axis length to that of their long at the same visual field is presented.The experimental results indicate that the wax appearance point and precipitation peak temperature of Linyuan crude oil with and without dilution is 50～45℃ and 40～30℃ respectively；the wax precipitation process and behavior of the diluted crude can not be changed by the diesel treatment，the more the added diesel is and / or the higher the temperature is，the fewer the number of the wax crystals is，and the higher their symmetry is and the lower their dispersion extent is，therefore，the better the improvement of the low-temperature flowability for the treated crude is.All of these provide a basis for the further investigation to the synergetic effect between PPD and the diluent.

Key words: Daqing crude oil, diesel dilution, flowability, wax precipitation process, wax crystal microstructure