We firstly report an efficient and novel method to functionalize graphene with 4-aminophenoxyphthalonitrile and successfully compound them with poly(arylene ether nitrile) (PEN) to prepare nanocomposite films. Fourier transform infrared spectra (FTIR), Raman spectra, and atomic force microscopy (AFM) were employed to examine the surface functionalization of graphene. The resulting PEN nanocomposite exhibited significant increase in dielectric permittivity. For 3wt.% nitrile functionalized graphene reinforced PEN nanocomposite film, the dielectric constant increased from 3.2 to 17.8 at the frequency of 1kHz. In addition, the PEN nanocomposite films showed low dielectric loss and good flexibility. This opens a new route to optimize interface structures and improve the comprehensive performances of graphene–polymer nanocomposites.