Single phase Sialon was synthesized successfully from fly ash by carbothermal reductionnitridation reaction in this paper. The effects of synthesizing temperature (1200°C, 1300°C, 1400°C and 1450°C) and carbon content (stoichiometric content, exceeding 10%, 50% and 100%) on the final production were studied by XRD and SEM. Synthesis mechanism of β-Sialon was also analysized. The results indicated that single phase β-Sialon with z=3 was obtained using fly ash as raw materials and carbon black of stoichiometric content as reducer by carbothermal reduction- nitridation reaction in flow nitrogen at 1450°C for 3h. Temperature and content of carbon had significant effect on the synthesis of β-Sialon.