An octagonal structure lithium niobate electro-optic deflector with quadrupole electrodes is designed in this paper. The electric field distribution characteristics of the octagonal structural deflector with quadrupole electrodes and ideal electrode structure are simulated and analyzed. The influences of structural parameters on the electric field distribution, field intensity gradient, and effective aperture ratio of the deflector are discussed. The selection method of structural parameters of the quadrupole electrodes octagonal deflector is proposed. Simulation results show that, under the same crystal and applied voltage, the electric field distribution of the octagonal structural deflector with quadrupole electrodes and ideal electrode structure are consistent in the paraxial region, and the field intensity error is less than 10%. According to the analysis results, an octagonal lithium niobate crystal electro-optic deflector is designed and developed. Experimental results show that the deflection sensitivity of the deflector is 0.312 μrad/V, which is consistent with the theoretical value of 0.340 μrad/V.