Nowadays, metal soft magnetic materials are mainly used in electronic components such as high-frequency inductors. Since all the elements in the soft magnetic alloys are transition metals, dense oxide layer is easily formed on their surfaces, which can affect the regulation of soft magnetic properties. In order to solve the problems, in this work, an innovative high-temperature pretreatment process in H₂/Ar mixture is adopted to pretreat FeNiMo raw powders. We confirm that the high temperature treatment in reducing atmosphere can effectively remove metal oxides from the FeNiMo material surface and increase the content of elemental states, thereby further significantly improving the effective permeability of FeNiMo raw powders. The pretreated FeNiMo powder is evenly coated with SiO₂ layers, forming the FeNiMo/SiO₂ soft magnetic composites. Compared with the untreated FeNiMo powder coated with SiO₂, the FeNiMo/SiO₂ pretreated with H₂/Ar mixture gas at high temperatures has high effective permeability and low loss. Our FeNiMo/SiO₂ cores prepared by the synergistic effect of high-temperature pretreatment process in H₂/Ar mixture and insulation coating process have more excellent soft magnetic properties than other iron-based soft magnetic composites. Therefore, the insulation coating after being pretreated at high temperature in reducing atmosphere can greatly improve the permeability and reduce the core loss of soft magnetic composites. This will provide a new strategy for enhancing the soft magnetic properties of the composite cores.