Silicon oxynitride ( Si2N2O) is a high-performance refractory and high-temperature structural material, which has advantages such as excellent creep resistance, corrosion resistance, and oxidation resistance. In this work, diatomite was used as silicon source, acetylene carbon black was used as reducing agent, and the Si2N2O/ SiC composite powders were synthesized in situ on the surface of diatomite through carbothermal reduction nitridation method. The samples were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy ( SEM), and N2 adsorption / desorption isotherms. The results indicate that under the condition of raw materials ratio m(diatomite) ∶ m(acetylene carbon black) = 1 ∶ 1, the SiO2 completely transforms into Si2N2O and β-SiC after calcination at 1 450 ℃ for 4 h, and the sample shows a spherical morphology with mesoporous structure, while a large number of layered small particles distribute around the large particles. As a high-performance high-temperature structural material, Si2N2O/ SiC composite powders could be a promising candidate for application in the field of structural composite materials.