A series of reactive pour point depressants (PPD) with anhydride group were prepared, and their action mechanism had been investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC) and cross-polarized light microscope. The results showed that the prepared pour point depressants had obvious pour point depressing effect on crude oil. Its action mechanism was concluded that PPD could react with the resin and asphaltene in the crude oil to generate a new macromolecule when crude oil was treated with PPD-3 at 90 degrees C. The new macromolecule further formed a new agglomerate structure by association with the asphaltene and resin in crude oil, which worked as a new nucleator to provide nucleation sites for wax crystal instead of the original asphaltene-resin agglomerate structure, and then improved the flowability of crude oil. (C) 2014 Elsevier Ltd. All rights reserved.