Abstract: Quantitative research on modification process of PPD-added crude oil is made through X-ray diffraction technique.Results show that wax crystallization types of crude oil for origin crude oil and PPD-added crude oil are all orthorhombic system.However, the size of wax crystallizations for PPD-added crude oil are larger than that of origin crude oil; the inter-planar spacing of crystallizations for PPD-added crude oil is less than that of origin crude oil; the wax crystallizations of PPD-added crude oil are more compact than that of origin crude oil, which is helpful for improving rheological characteristic of crude oil; inter-planar spacing of crystallization increases with the temperature in vertical carbochain, but the inter-planar spacing of crystallizations are not related to the temperature increase in parallel carbochain.