In order to prepare Ag/SiO2 conductive powder with dense and uniform coating, which is not easy to fall off and has good binding ability with resin, Ag/SiO2 electromagnetic shielding coating with excellent performance can be obtained. Pretreatment with sensitizer, coupling agent modification, and polymer surface coating respectively. Use glucose as reducing agent and ammonia water as Ag+ complexing agent for electroless silver plating to prepare Ag/SiO2 microbeads. The electrical conductivity of the composite powder was tested, and the reaction mechanism of the pretreatment and the growth mechanism of the silver layer were analyzed based on experimental phenomena. Scanning electron microscope and X-ray diffractometer were used to characterize and verify Ag/SiO2 microbeads with different pretreatment methods. The Ag/SiO2 microbeads prepared by different pretreatment methods are used as fillers, unsaturated polyester resin is used as the matrix to prepare conductive coatings, and the bonding properties of different Ag/SiO2 microbeads and coatings and the effects of filler content on the conductivity of the coatings are studied. The results found that the silver layer of Ag/SiO2 microbeads prepared by the sensitization pretreatment method is uniform, dense, and no shedding, which is significantly better than the other two pretreatment methods. The compaction resistance can be as low as 144.04 mΩ, and the Ag/SiO2 microbeads when the filler content is 80%, the optimal conductive path can be formed, the volume resistivity can be as low as 0.0051 Ω.cm, and the electromagnetic shielding efficiency can reach 51.9 dB when the electromagnetic wave frequency is 8.2~12.4 GHz. It is concluded that the sensitization method can be used to plate the surface of the glass beads with a high-quality silver layer, which has good electrical conductivity in the resin system. It can be used as a high-quality electromagnetic shielding agent for the preparation of conductive coatings. The prepared electromagnetic shielding coating has excellent shielding effect.