Abstract: Carbon nanotubes(CNTs) were modified by Fe₃O₄, the dispersibility of CNTs in polyvinylidene fluoride (PVDF) and interfacial adhesion were improved so as to achieve high mechanical properties and electrical properties, better application for sensor, actuator and energy storage with functional performance. Fe₃O₄-CNTs were prepared by in situ hydrothermal synthesis method. Fe₃O₄-CNTs/PVDF composites were prepared by the casting process. The structure and crystallization behavior of Fe₃O₄-CNTs/PVDF composite films were studied by SEM, TEM, XRD and DSC. The mechanical properties, the dielectric properties and breakdown field strength of Fe₃O₄-CNTs/PVDF composite were studied by DMA and the broadband dielectric spectrometer. The results show that, due to the adding of Fe₃O₄-CNTs, the crystallinity of the composite is improved and the PVDF β crystal phase is observed for adding Fe₃O₄-CNTs. The dielectric constant is increased, the increase of dielectric loss is inhibited. The breakdown field strength is increased visibly.