Abstract: In response to the high cost and complex processing of talc powder, as well as the large production volume but low utilization rate of steel slag, ultrafine vertical grinding technology combined with functional additives was employed to successfully process steel slag shield powder with a median diameter (d₅₀) of 6.445 μm (600 mesh), 5.775 μm (800 mesh) and 5.098 μm (1000 mesh) respectively. The preparation of shield powder/stone-plastic composite materials were achieved by substituting shield powder for talc powder through a process that integrates melt blending with hot and cold pressing techniques. Tensile strength, bending strength, and impact strength tests were conducted on these materials, and characteristics were analyzed using XRD, SEM, FTIR, and DSC. The results indicate that the incorporation of shield powder significantly enhances the mechanical properties of the stone-plastic composites. Particularly, when the substitution ratio of shield powder for talc powder reaches 50%, the tensile strength is increased by 12.3%, 33.2%, and 27.4%, the bending strength by 11.7%, 26.0%, and17.6%, and the impact strength by 33.3%, 52.9%, and 32.8%, respectively, compared to the composites made with pure talc powder. Due to its narrowest fineness distribution width (2.177), the 5.775 μm shield powder exhibits excellent dispersibility in stone-plastic composite materials and significantly improves interfacial compatibility, thereby demonstrating the most pronounced performance in enhancing the mechanical properties of the stone-plastic composite materials. Additionally, the 5.775 μm shield powder effectively increases the melting enthalpy and crystallization enthalpy to 45.16 J·g⁻¹ and 42.31 J·g⁻¹, respectively, which aids in the formation of a more uniform crystal structure in the stone-plastic composite materials, promotes nucleation and crystal growth, and further enhances their mechanical properties.