Abstract: The energy conversion in dynamic process of a CFB boiler unit was studied, calculated and compared quantitatively based on analysis of the energy storage features, so as to obtain the evaluation index of economical coal feed rate through comparison between the economical and actual coal feed rate, and to investigate the effects of dynamic process control. In addition, the fluctuation status of main steam pressure was used to reflect the dynamic energy balance, which was verified by two examples of load-up processes. Results show that both the study of energy conversion in the process of CFB boiler load changes and the application of evaluation index for economical coal feed rate in the control of air-coal ratio are conducive to the safe and economic operation of the CFB boiler. This may serve as a reference for the control of boiler load changes.