An electrical absorption graphene modulator based on hybrid plasmonic waveguide is theoretically demonstrated. The sidewall scattering loss is mostly restrained by the vertical metal-insulator-silicon (MIS) waveguide structure. The patterned Si3N4 (SiN) can both serve as the mask and the insulation layer, which offers the direct formation of silicon stripe by thermal oxidization. The metal cap layer utilized as an electrode is favorable to improve the frequency response. By finite element method (FEM) optimization of waveguide dimensions, the 700 nm-wide optical 3 dB-bandwidth that ranges from 1200 to 1900 nm can be obtained at the modulation length of 30 μm. The propagation loss is reduced to 0.088 dB/μm. The modulation depth and power consumption are calculated to be 0.509 dB/μm and 61.3 fJ/bit, respectively. The estimated electrical 3 dB-bandwidth of 330 GHz promises the proposed modulator potentials in next generation on-chip optical signal processing.