Abstract: The graphene functionalized by benzyl acid (BFG) was prepared based on graphene oxide (GO). The structure and morphology of BFG were characterized by IR and XRD. BFG, as a kind of flame retardant synergist, was added to Al(OH)₃/polypropylene (PP), in which Al(OH)₃ was used as the flame retardant. The effect of mass ratio of BFG to Al(OH)₃ on the flame retardancy and mechanical properties of BFG-Al(OH)₃/PP composites was studied. The limiting oxygen index (LOI) test, thermogravimetric analysis, cone calorimetry analysis, tensile test and residual carbon scanning analysis were progressed to investigate the flame retardancy and mechanical properties of BFG-Al(OH)₃/PP composites. The results show that the flame retardancy and mechanical properties of 1.5wt%BFG-38.5wt%Al(OH)₃/PP composite are the best, whose LOI is 24.6%, tensile strength is 20.64 MPa, respectively, and its thermal release rate peak and total heat release is reduced by 51.5% and 18.6% compared with the pure PP sample, respectively.