Consisting of steam cooler, condensation zone and drain cooler, the three-stage feedwater heater is widely used in the thermal power plants. To study the variable condition characteristics of three-stage feedwater heater with water level controlled, a GSE simulation model of that in 300MW thermal system of power plant was established. Validated by the steady states of the heater, different dynamic characteristics were investigated when the load varied. The results revealed that the steam pressure, feedwater flow and feedwater inlet temperature drops would have a significant influence on the extracting steam flow, feedwater temperature increment and terminal temperature difference. The dynamic trends were intensified with the variation of the input condition enhanced. The response time of extracting steam pressure drops is 430s and that of feedwater flow drops would be prolonged to 600s. The dynamic processes with water level controlled were carried out and showed that adjusting flow valve could keep the water level stable and secure the operation of heater smooth and steady. However, frequently controlling the position of flow valve could impair the steady procedures of other parameters and prolonged the response time.
