We propose a high-performance, graphene-based optical modulator with a surface plasmon resonance (SPR) at 1550 nm. In the proposed device, a graphene layer is embedded in a hybrid plasmonic waveguide to enhance the light-graphene interaction. The adjustment of the permittivity of the graphene causes a significant modulation of the absorption in the SPR through a variation of the field confinement in the graphene layer, in addition to a resonant angle shift. With an optimal thickness of a metal (Ag) film and the properly chosen operation point of the Fermi level of graphene, a modulation depth of ∼100% was achieved. As the number of graphene layers in the proposed device increases, the insertion loss decreases. With five-layer graphene, a 6% insertion loss was achieved.