The interdigital electrode is expected to improve the optical performance of the liquid crystal clad optical waveguide by simplifying the waveguide layer structure. Therefore, a physical model of the liquid crystal clad optical waveguide based on the interdigital electrode is established in this paper, and the changes of the effective refractive index modulation of the waveguide mode under this structure are studied. Firstly, the electric field distribution characteristics of the interdigital electrode are defined by theoretical simulation. Then, the configuration of liquid crystal molecules under electric field and its effect on the waveguide mode effective refractive index are analyzed, and the effects of the initial orientation angle, Δn, Δε on the waveguide mode effective refractive index are quantitatively studied. Finally, the effective refractive index modulation performance of the liquid crystal optical waveguide is compared between the interdigital electrode and the traditional two-sided electrode structure. The results show that the interdigital electrode produces periodic electric field distribution, and the rotation angle of the liquid crystal and the effective refractive index distribution of the optical waveguide are periodic. Compared with parallel orientation (initial orientation angle 2°), the effective refractive index modulation amplitude of vertical orientation (initial orientation angle 88°) is larger, and the effective refractive index modulation amplitude of vertical orientation is 10.1 times that of parallel orientation at 40 V voltage. Larger Δn and Δε are helpful to obtain larger effective refractive index modulation of optical waveguide. Compared with bilateral electrodes, interdigital electrodes can achieve a larger effective refractive index modulation at the same voltage.