The invention discloses a monitoring system and method for heat released from a hearth of a circulated fluidized bed boiler, and belongs to the technical field of burning of a circulated fluidized bed. The system comprises a data communication and processing device, an industrial analyzer, a coal heat meter, a coal feed quantity detection device, a limestone powder feed detection device and a bed temperature detection device. The data communication and processing device is used for monitoring heat released from the hearth of the circulated fluidized bed boiler and comprises a communication module, a coke burning module, a volatile combustion module and a limestone desulfuration module. Heat released by burning of coke in the hearth, heat released by burning of volatile precipitation and combustion and heat released in the limestone desulfuration process are calculated and accumulated, so that the total released heat in the hearth is obtained. Monitoring on the heat released from the inside of the hearth of the circulated fluidized bed boiler has an important guidance significance to safe and efficient operation of the boiler.