Stockpiled high carbon-content fly ash and lime was used to prepare belite cement by hydrothermal reaction followed by low temperature calcination. Sodium hydroxide was added as an activator to accelerating the reaction. 0-1.5 wt% Na2O equivalent NaOH was added as a aqueous solution into the mixture of 20 wt%-35 wt% CaO and 65 wt%-80 wt% fly ash. The mixture was formed into granules and steam-curing the at 97°C for 12 h, followed by heating at 800°C for 1 h. The results show that adding 1.0 wt% Na2O to the mixture of fly ash and CaO can efficiently promote the hydrothermal reaction. Belite cement with practicable strength and characterized by rapid setting and high sulfate attack resistance was synthesized.