Abstract: Using steam-water distribution equation, the variations of extraction flow caused by condensate throttling were calculated for each stage of unit, based on which two boundary models were set up for the relationship between turbine power output and condensate water flow, so as to determine the range of load change by condensate throttling. On the basis of analyzing the water temperature change in deaerator, the maintain time of condensate throttling under present water storage was obtained, which was subsequently verified by a 600 MW unit. Results show that condensate throttling would double the rate of load change in power plants; moreover, the load change capability would be stronger when the unit load is higher, in the case of same throttling rate.