Abstract: The half-wave voltage and bandwidth of the electro-optic modulator depend mainly on its electrode structure. The difference of refractive index between the waveguide and the substrate of the modulator based on the lithium niobate on insulator (LNOI) is about ten times of the traditional technique, which can significantly improve the overlap degree of light field and electric field, reduce the half-wave voltage, and improve the bandwidth. Therefore, it is urgent to optimize the electrode design of this structure. In this paper, COMSOL Multiphysics and HFSS were used to simulate and optimize the electrode of intensity modulator based on LNOI structure. The effects of electrode width, electrode thickness, electrode gap, upper and lower cladding thickness on the characteristic parameters of the modulator were discussed. Then, the parameters of the modulator, such as electro-optic overlap integral, microwave effective refractive index, microwave attenuation coefficient and electrode characteristic impedance, were obtained. On this basis, these performance parameters were optimized to improve bandwidth and reduce half wave voltage. Results show that the half-wave voltage reaches 2.17 V, and the bandwidth of 3 dB is better than 70 GHz when the electrode length is 1 cm. The proposed work has important significance for the electrode design of LNOI-based electro-optic modulator.