The ever-growing demands to compute information, store, and communicate generate a continuous driving force for transformative photonic technologies. On chip photonic integrated circuits (PICs) founded a roadmap for scaling down photonic modules to meet the challenges of bandwidth enhancement and power reduction. However, it also produces an even critical need for state-of-the-art devices and better materials. Lately, the material group of transparent conductive oxides (TCO) has appealed attentions for on-chip photonic components. In specific, indium tin oxide (ITO) has been found to have active large refractive index variations, which creates possibilities to realize high speed Electro-Optic (E-O) modulation of sub-diffraction device scales. This ITO based tapered plasmonic waveguide devices will combine the large E-O absorption effects of ITO with the localized SPPs and the ultra-strong optical field confinement. In this paper, we design the device which is fabricated on commercial silicon-on-insulator (SOI) platform integrated with a 3μm long, 300nm wide gold plasmonic slot waveguide, which can dynamically switch the optical transmission from high absorption mode by enhanced plasmonic E-O absorption to low loss mode. The active E-O modulation region consists of a metal-HfO2-ITO capacitor that can electrically switch the ITO into ENZ with ultra-high modulation strength of 2.62dB/μm in simulation and 3.5dB extinction ratio in experiment. We also demonstrated the EA modulator a relative uniform E-O modulation within 1530~1600nm wavelength.