Abstract: This study investigated the effects of dual magnetic field regulation on diamond film growth using DC arc plasma jet CVD through COMSOL simulations and experiments. Simulations revealed that magnetic fields optimize particle trajectories in the plasma, enhancing reactive radical concentration and distribution uniformity on the substrate. High-speed imaging and optical emission spectroscopy confirmed these findings, demonstrating that magnetic fields increase radical density while improving spatial homogeneity. Under the dual magnetic field effect, the synthesized 8-inch diamond film exhibits improved grain size and thickness uniformity. The deviation between thickness at various positions across the entire substrate surface and the average thickness value is reduced to within 10%, while demonstrating a (220) preferred orientation. Radial sampling at 20 mm intervals showed an average thermal conductivity of 1916.4 W/(m·K) and a post-polishing transmittance of 68.9% at 10.6 μm wavelength, with all samples deviating within 2.0% from mean values, confirming outstanding material uniformity.