Surface plasmon resonance (SPR) enables strong field confinement, opening thereby new avenues for device miniaturization and reducing energy consumption. Plasmonic devices with electrical tunability attract tremendous interest for various applications. Most of the current researches achieved SPR modulation with relatively large driving voltages, or by other relatively low-speed tuning approaches, such as thermo-optic, magneto-optic, acousto-optic etc. In this paper, we propose and demonstrate an efficiently electrical SPR modulation based on lithium niobate (LN) with gold nanolayer (~81 nm) via electron-plasmon interaction. Efficient intensity modulation and wavelength shift (in visible band) of ~5.7 dB/V and ~36.3 nm/V are respectively obtained with low DC current. More importantly, modulation phenomenon of field distribution dependent is also observed and experimentally unveiled. Further performance is analyzed in terms of AC modulation and polarization characteristics. This key achievement opens up opportunities for applications such as optical interconnection, electric field sensing, electrically plasmonic modulation, etc.