Because of its high strength and high toughness, graphene has been widely used in mechanical reinforced composites. In general, the mechanical enhancement depends mainly on the properties of graphene itself and the number of surface chemical functional groups attached on it. In this paper, we report a method to improve the mechanical performance of polymer by using a kind of functionalized reduced graphene oxide (F-RGO), i.e., the F-RGO is prepared by chemical treatment, and then the F-RGO/polyvinylidene fluoride (PVDF) composite films are obtained by spin coating. Because the chemical treatment can increase the number of functional groups on the surface and edge of F-RGO, these functional groups make the F-RGO sheets strongly coupled with PVDF molecules, so as to achieve the purpose of mechanical enhancement. The experimental results reveal that the mechanical properties of the F-RGO/PVDF composite films are improved for 42% times, when comparing with regular RGO/PVDF composite films.