Abstract: Improvement of loading change rate in coal-fired power units is one of the key evaluation index of flexibilities in the power system during automatic generation control (AGC) regulating processes. In this study, the dynamic simulation models of a 660 MW supercritical reheat coal-fired power unit were developed with the detailed control systems embedded. Then, the dynamic characteristics of main thermal parameters at different loading change rate ranging from 75% to 100% THA were obtained. Taking the maximal fluid temperature deviation and average standard coal consumption rate deviation as the evaluation indexes, the security and economy of the coal-fired power units during AGC load change processes were analyzed. The results reveal that with the increase of loading change rate, the output power, main steam temperature and reheat steam temperature fluctuate more drastically. Besides, the maximal fluid temperature deviations increase gradually at water wall outlet, platen superheater outlet, horizontal low-temperature reheater inlet, and vertical low-temperature reheater outlet, which are 24.7, 29.1, 26.1, 41.3 °C, respectively. The average standard coal consumption rate deviation decreases when the loading up rate increases, ranging from 2.35 to 2.53 g/(kW·h). On the other hand, the absolute value of average standard coal consumption rate deviation decreases when loading down rate goes up, ranging from –2.64 to –2.50 g/(kW·h).