We report a graphene-assisted near-field radiative thermal rectifier (GTR) made of a graphene-covered VO2 plate and a silicon dioxide (SiO2) plate separated by a vacuum gap. In framework of fluctuating electrodynamics and fluctuation-dissipation theorem, a comprehensive calculation is performed on near field radiative heat flux at different chemical potential values and different vacuum gaps. The near field radiative thermal rectifier (TR) made of a VO2 plate and a SiO2 plate separated by a vacuum gap is also included for comparison purpose. Being compared with TR, GTR with 0.3 eV chemical potential has a great advantage in total rectification factor phi under 200 nm vacuum gap when hot and cold temperatures of the rectifier are kept at 353 K and 300 K, respectively. Total rectification factor phi as high as 3.8 for GTR can be reached at 10 nm vacuum gap and 0.3 eV chemical potential due to strong interplay between p-polarized surface plasmon polaritons (SPPs) of graphene and p-polarized surface phonon polaritons (SPhPs) of SiO2 when hot and cold temperatures of the recitfier are kept at 353 K and 300 K, respectively. This value amounts to almost 1.69 times that for TR at same conditions. This work will pave a way to further improve performance of near-field radiative thermal rectifier and be valuable to research in near-field radiative thermal management and modulation. (C) 2017 Elsevier Ltd. All rights reserved.