The capacity of power grid in China increases rapidly. Because of the reliability of multi-infeed DC system in the grid, power system damping is relatively weak. Realizing isolated island operation of thermal power units with FCB (fast cut back) ability is considered to be the best solution of quick restoration of power grid. Taking a 1000MW USC (Ultra-supercritical) unit as an example, based on the data of the unit’s load refection tests, this paper conducts a look at several aspects of research: (1) predicting the maximum speed rise of rotor during FCB process with different loads by using Simulink; (2) predicting the water level of deaerator and condenser during FCB process with different loads by same method; (3) predicting the highest exhausted steam temperature of HP cylinder during FCB process with different loads by using FEM; (4) comparing these key parameters with FCB test data, it shows that the predicted results agree with test data very well. (5) analyzing the influence of FCB test on the safety and life loss of the thermal equipment.Copyright © 2014 by ASME