Integrated modulators are essential components for optical sensing and communication applications. However, most efforts have been focused on infrared telecommunications wavelengths, with very little consideration for visible light applications. Here, we design an electro-optic (EO) modulator at 532 nm with the waveguides formed by SU8 polymer structures on the thin-film lithium niobate (LN). The simulation results show a low loss, high modulation efficiency, and large bandwidth simultaneously for the modulator. The predicted low loss is attributed to the LN etchless waveguide and high coupling efficiency, i.e., 93%, with the single-mode fiber theoretically using a SU8 edge coupler. The simulated low voltage-length product of 1.15  V  ·  cm and a 3-dB-bandwidth of >120  GHz at a length of 5 mm are superior to any other modulator in the optical communication band. The modeling of the modulator proposed here shows great potential for visible light communications applications such as energy-efficient and large-capacity underwater wireless optical interconnects.