β_Sialon powder was prepared from fly ash and carbon black via carbothermal reduction nitridation in this study. The main factors such as additives of Al2O3 and carbon, heating temperature, soaking time and the flow of N2 were investigated and their effects on the phase of products were also analyzed by XRD and SEM. A nearly pure β-Sialon powder can be obtained when aproper amount of Al2O3 is added, carbon is 23%, and calcination occurs at 1 450℃ for 6 hours at the N2 flow of 2.0 L/min. Some other phases such as AlN, β-SiC, Si3N4, Al6Si2O13, O'-Sialon, α-Al2O3, SiO2 existunder different preparation conditions. The size of β-Sialon powder is mostly 1～3 μm, and the shape and crystallization degree of prepared β-Sialon are greatly affected by the synthesized conditions.