The use of a low pressure economizer (LPE) is an effective way to recover waste heat from the exhaust flue gas in thermal power plants. In this paper, an improved bypass staged economizer scheme is presented for China's 600-MW ultra-supercritical power units. The simulation models of the bypass staged economizer and traditional LPE were established based on a 600-MW unit. The simulation results showed that when the presented economizer system was adopted, the temperature of the exhaust flue gas was reduced to near the flue gas acid dew point, thereby greatly improving the energy-saving effects. Compared with the traditional LPE system, the improved economizer system can reduce standard coal consumption rate by an additional 1.1 g/kWh. The bypass ratio under different loads could be adjusted to achieve the best energy-saving effect. The optimum bypass ratio was analyzed under different loads. The results showed that the improved economizer system had a better energy-saving effect by actively controlling the exhaust flue gas temperature. (C) 2018 Elsevier Ltd. All rights reserved.