To investigate the effect of modified graphene (Gra) by poly(methoxy poly(ethylene glycol) monomethacrylate-co-l-vinyl-3-ethylimidazolium bromide) (P[MPEGMA-IL]) on crystallization and dielectric behavior for poly (lactic acid) (PLA), the neat PLA and its composites were fabricated via solution blending and hot pressing. P [MPEGMA-IL.] can improve the dispersibility of Gra in PLA matrix. The crystallization rate of PLA composites was increased with increasing the content of P [MPEGMA-IL] and Gra due to the plasticizing effect of P [MPEGMA-IL] and the nucleating effect of better-dispersed Gra. In the frequency spectra of PLA composites treated by cold crystallization process, cc relaxation and interfacial polarization resulted in high values of dielectric permittivity. The incorporation of modified Gra into the matrix can accelerate interfacial polarization. The effect of modified Gra on charge carrier movement mechanism was resulted from the increase of the mobile charge carriers at the interphase and the dielectric strength of interfacial polarization.