The oils studied in this work were three typical oils, sampled from Daqing, Jilin, Liaohe Oil Fields and marked with 1#, 2#, 3# respectively, with wax contents 20.06%, 26.2%, 32.9% separately. The effects of PPD on WATs, abnormal points, pour points, rheological properties and wax-crystal morphology were studied in detail in this paper. The results of experiments indicated that PPD lowers WATs and abnormal points, and decreases the viscosities of crude oils when they are non-Newtonian fluids. In wax-crystallization peak area, both high shear rate and increase of cooling rate make the effects of PPD decrease and the viscosity of oil increase. When 1# sample is reheated to some temperature below 50°C (for 2#, below 70°C), the effects of PPD reduce. With the increase of PPD’s dosage, the crystal size gets smaller and the dispersibility becomes better.