The dilution water blending is a key link in the crude oil electrical desalination system of oil fields or refineries, which directly affects the efficiency and operating energy consumption of electrical desalination. In order to further simplify the equipment structure, reduce costs and increase system efficiency, a thin plate static mixer for dilution water mixing was proposed. On the basis of the preliminary structural design of the thin plate static mixer, computational fluid dynamics (CFD) was used to perform three-dimensional numerical simulation of oil-water mixing, the square root of segregation strength (IOS0.5) in a uniform mixing state and pipeline pressure drop (Δp) were used as evaluation parameter, which can indicate the influence of structural parameters on the uniformity of oil-water mixing and the running energy. The structural parameters were the length of water injection pipe, the distance between water injection pipe and thin plate, thin plate guide position and the thickness of bending sheet. Subsequently, with the inner diameter D of the hybrid pipeline as a reference, the key structural parameters were optimized by the response surface method (RSM), and the mixing performance under the optimal combination of structural parameters was predicted. The optimal combination of structural parameters obtained by optimization was as follow: the length of the injection pipe was 1/3D, the distance between the center of the injection pipe and the orifice was 4/25D, the guiding position of the orifice was 1/8π, and the thickness of the orifice was 1/25D. By comparing and analyzing the mixing effect of the thin plate static mixer before and after optimization, it was found that the optimized structure of IOS0.5 was 43.06%, which was lower than before optimization. Qualitative analysis of the water phase velocity cloud diagram and streamline diagram in the thin plate mixer showed that when the water injection ratio was 2%, the oil and water two phases can reach a uniform mixing state at the 3D downstream of the water injection pipe. It can be seen that the thin plate static mixer can quickly achieve uniform mixing of oil and water at a small water injection ratio.