Abstract: The organic sol-gel is a research hotspot for the synthesis of ultrafine boron carbide powders at low temperature. Based on this technology, trimethyl borate is used as a raw material for pyrolysis. Compared with organic sol-gel technology, the gel formation process is omitted and the operation flow is simplified. Based on the XRD and SEM analysis of the products, the effects of reaction temperature, reaction time, tableting pressure and rising-cooling rate on the purity and morphology of the products were further investigated. The analysis results show that among all the above research factors, the reaction temperature and rising-cooling rate play a major role in the formation of uniform and submicron-sized boron carbide products. Uniform boron carbide products with a particle size distribution of about 1 μm are obtained at a high temperature of 1 600 ℃ and a rapid rising-cooling rate of 400 ℃/min.