Abstract: In the field of aluminum matrix composites, Si C is a commonly used reinforcing phase particle, but its surface usually has a high surface energy, and it is difficult to give full play to its performance enhancement effect on the matrix by directly using Si C particles as the reinforcing phase, so pretreat work is usually necessary for Si C. The effects of powder pretreatment process of high temperature oxidation on the microstructure and mechanical properties of selective laser melting（SLM）-fabricated Si C/Al Si10Mg composites were systematically investigated. By comparing phase composition,densification, grain orientation, and mechanical behavior between untreated and high-temperature-oxidized Si C specimens,the regulatory mechanisms of pretreatment on the material performance were elucidated. The results show that the SiO₂ film formed on oxidized Si C particles effectively suppresses detrimental interfacial reactions（e.g., Al₄Si C₄ phase formation） between Si C and molten Al matrix, reduces porosity, and mitiga tes stress concentration. Consequently, the preoxidized composite achieves enhanced compressive strength of 584.7MPa, tensile strength of 424.6 MPa and elongation of 5.2%,while the those of the composite are 574.5 MPa, 397.2 MPa and 1.8%, respectively. The oxidation of Si C particles inhibits the in-situ reaction between SiC and molten Al matrix, therefore inhibits the eutectic Si coarsening and reduces the microvoid defects. This work provides theoretical and experimental foundations for optimizing SLM-processed high-strength aluminum matrix composites.