The effect of core-shell SiO₂@(1,2-PB/EPDM) particles on the properties of the polyolefin composites was investigated in this paper. Core-shell particles SiO₂@(1,2-PB/EPDM) were prepared by acid activation, silane coupling agent KH-570 modification and precipitation polymerization. The core shell particles were added into the polyolefin resin, stirring and dispersing evenly. The polyolefin composite filled with glass fiber cloth reinforced core-shell particles SiO₂@(1,2-PB/EPDM) was prepared by dipping glass fiber cloth into composite adhesive solution and hot pressing. The effects of different shell thickness on mechanical properties, dielectric properties and water absorption of the composites were investigated. The results show that with the increase of shell thickness, the flexural strength and flexural modulus of the composites increase, and the dielectric constant, loss factor and water absorption decrease. When the thickness of the polymer shell is 60 nm, the dielectric constant of the composite is 3.44, the loss factor is 3.46×10^-3, the water absorption is 0.064%, the flexural strength is 178.8 MPa, and the flexural modulus is 16.57 GPa. The comprehensive performance of the polyolefin composites can meet the requirements of microwave substrate materials.