Abstract: Lead/boron carbide/boron phenolic resin (Pb/B₄C/BPR) is a new kind of shielding composite with high temperature resistance and high shielding performance for radiations. In this paper, the effects of lead powder content, particle size and surface treatment (SiO₂ coating) on the linear coefficient of thermal expansion (CTE) and mechanical properties of the composites were systematically studied. The results show that the composites have the smallest linear CTE and excellent comprehensive mechanical properties when the lead powder content is 36% (volume fraction) and the particle size is 38 μm. Proper coating of SiO₂ on the surface of lead powder effectively reduces the density difference between lead powder and B₄C powder, which not only significantly reduces the linear CTE of the composites, but also improves the tensile, flexural strength and impact toughness. However, too much SiO₂ coating content will result in the linear CTE of the composites increasing and the tensile, flexural strength and impact toughness reducing.