Nanocomposite pour point depressants (PPDs) provide a new way to further improve the fluidity of waxy crude oil at low temperatures, which has important application values in pipeline transportation. In this work, the effect of ethylene vinyl acetate (EVA) doped with magnetic spherical nanoparticles of Fe3O4 (30 nm) on the morphology of wax crystals and the flow behavior of Daqing crude oil was investigated by polarized optical microscopy and rheological testing. The results showed that, compared to the EVA PPD doped with spherical nano-SiO2 (with the same size), the EVA (VA = 28%)/Fe3O4 nanocomposite PPD caused Daqing crude oil to have a more compact and regular wax crystal structure and a weaker gel structure because of the synergistic effect of magnetic materials and heterogeneous nucleation. This study examines the mechanism of nanocomposite PPDs and provides a new perspective for the development of new nanohybrid PPDs.