Abstract: In response to the problems existing in the original deep coupled waste heat utilization system of a 660 MW coal-fired unit, the reasons for the failure to achieve the design goals of the system were analysed. Four optimization and renovation schemes were strategically adopted, including the optimization of bypass flue, the optimization of water intake position for condensate heat exchanger, the optimization of recirculation pipeline and adding a water side bypass for the flue gas cooler. The final optimization and renovation effect was calculated and analysed in detail. Results show that, after the optimization, the proportion of bypass flue gas volume increases to 13.5%, the inlet water temperature of the condensate heat exchanger can be stabilized at 70 ℃ for a long time, and the steam consumption of the auxiliary steam heat exchanger is basically reduced to 0. After optimization, the system is put into operation to reduce the net coal consumption rate of the unit by 2.73 g/(kW·h).