Abstract: For the better utilization of vapor grown carbon fiber (VGCF) as the reinforcing material in polymer matrix composites，the VGCF surface was modified by three methods，the two-step treatment with hydrogen peroxide and concentrated nitric acid，treatment with the silane coupling agent，and the treatment with hydrogen peroxide and concentrated nitric acid combined with the silane coupling agent，respectively. The effects of surface modification on the microstructure of VGCF were studied and comparatively analyzed by AFM，FTIR，TG and XRD. The results show that the three modification methods have no significant effect on the crystal lattice of VGCF. Oxygen-containing groups such as carboxyl groups can be grafted onto the surface of VGCF through the two-step treatment with hydrogen peroxide and concentrated nitric acid. And siloxane oligomer can be grafted on the surface of VGCF through the modification with silane coupling agent. More siloxane oligomers can be grafted onto the surface of VGCF by the treatment with hydrogen peroxide and concentrated nitric acid combined with the silane coupling agent，which may be of great benefit to the improvement of the compatibility between VGCF and polymer matrix materials.