TiB2-SiC composite powders were synthesized by carbothermal reduction using silica sol, carbon black, TiO2 and B4C as the raw materials. The effects of reaction temperature and titanium oxide content on the phase composition and morphology of TiB2-SiC composite powders were investigated. Thermodynamic analysis and calculation were performed systematically during the reaction, and the growth mechanism of TiB2-SiC composite powders was discussed. The results have shown that the suitable condition for synthesizing TiB2-SiC composite powders is at 1 600 ℃ for 1h. In the reaction process, TiB2 is formed before SiC, and the formation of TiB2 alters the growth mode of SiC. When TiB2 content is about 10%, the formation of SiC is controlled by the vapor-solid reaction to the combination of vapor-solid and vapor-vapor reaction. The composite powders are mainly composed of a small amount of round-like particles, short rod-like particles and a lot of whiskers. With the increase of TiB2 content in the composite powders, the growth of SiC whiskers is inhibited. When TiB2 content is more than 20%, the number of whiskers in the composite powders reduces, and the number of round-like, plate-shaped and short rod-like particles increases noticeably, which results in a variety of the morphology. The growth of SiC is still controlled by the combination of vapor-solid and vapor-vapor reaction.