Reaction-sintering is a common process for the preparation of SiC ceramics, and the prepared SiC ceramics not only have superior performance and low sintering temperature, but also the shape and size of sample are not limited, which have a wide range of application prospects. However, The reaction-sintering SiC remains a lot of residual silicon, which seriously affects the high-temperature performance of material. In this study, the addition of Al₂O₃-Y₂O₃-SiO₂ sintering additive was used to reduce the residual silicon content. SEM, EDS, TEM and other analytical methods were used to study the effect of sintering additive on the structure and properties of reaction-sintering SiC ceramics. The results show that the sintering additive can effectively fill the grain boundary pores and improve the material properties. When the addition contnet is 1.5% (mass fraction), the fracture toughness and bending strength of sample reach 3.28 MPa·m^1/2 and 135.20 MPa. At the same time, the hardness and thermal conductivity also increase to 18.1 GPa and 18.60 W/(m·K). In addition, the presence of alumina and other phases in the sintering aids can effectively improve the stability of SiO₂ oxide film and reduce the oxidation rate, thereby avoiding film cracking and significantly improving high-temperature performance of SiC ceramics.