Abstract: In order to provide reference for design optimization of double-reheat boiler and operating temperature regulation, the effects of flue gas recirculation on combustion and heat transfer characteristics are studied based on a 660 MW double-reheat tower-type boiler by numerical simulation. The user-defined function approach predicates the CO reduction effect on NO_x. The numerical results show that it is optimal to simplify the convective heating surfaces into a plane among the three modeling methods for the upper heating surfaces in furnace. The recirculating flue gas could improve the burnout rate. The flue gas could shrink the high temperature area (1565~1700K) in burner area and improve the outlet temperature of low-temperature superheater. When the flue gas recirculation ratio increases to 20%, the oxygen concentration in the burner area and CO concentration at the hopper decrease. The NO_x emission at low temperature superheater outlet decreases from 143.69 to 94.07mg·m^-3 (6% O₂). The ratio of heat absorption of water-cooled wall to total heat absorption decreases by 3.50%, but those ratios of reheater, superheater and economizer increase by 2.53%, 2.13% and 0.54%, respectively. The heat flux is symmetrically distributed in the center line of the furnace. The peak of heat flux is about 330kW·m^-2. Flue gas recirculation technology shrinks the high flux area and improves the safety of boiler operation.