Abstract: In order to study the effect of crosslinking behavior on the dielectric properties of nanocomposites, polyethylene/montmorillonite (PE/OMMT) and crosslinked polyethylene/montmorillonite (XLPE/OMMT) are prepared by melting blending method. X-ray diffraction (XRD), Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) are used to characterize the properties of the samples. It is demonstrated that the spacing of layers of OMMT changes after being doped into polymer matrix, and the crosslinking of the polymer reduces the spacing of layers of OMMT. With heterogeneous nucleation of OMMT, the crystal morphology of nanocomposite dielectric will change from spherulite to transcrystalline. The amorphous area of XLPE/OMMT sample increases and the crystallinity decreases after crosslinking. The results of dielectric spectroscopy measurement show that the dielectric constant of the nanocomposites decreases with the increase of frequency. With the same OMMT content, the dielectric constant of XLPE/ OMMT composites after crosslinking is larger than that of the PE/OMMT nanocomposites. Because the crosslinked process affects the dispersion of OMMT in the matrix, the dielectric loss peak changes from unimodal to bimodal and the peak value increases. As temperature rises, the peak width of the double-peaks increases and the relaxation time distribution widens, the low-frequency peak disperses and the high-frequency peak moves to high frequency. The increase of OMMT content and the crosslinked process inhibit the dispersion of OMMT in the matrix, while the interfacial polarization and the loss of diversified groups change the dielectric spectrum and ther-mogram obviously.