Abstract: Taking a 200 MW tangentially-fired boiler as an object of study, numerical simulations were conducted on the pulverized coal combustion process respectively in pure air and oxy-fuel environment, by the computational fluid dynamics (CFD) combined with improved radiation model and chemical reaction mechanism. Based on analysis of the in-furnace combustion and heat transfer characteristics, the oxy-fuel combustion condition was optimized. Results show that high concentrations of CO tend to appear in dry flue gas recycling; the total radiative heat transfer in oxy-fuel combustion with 28.5% and 27.1% concentration of oxygen respectively under dry and wet flue gas recycling mode is nearly the same as that in pure air combustion; increasing the momentum of secondary air (SA) can effectively reduce the concentration of CO in the hopper area, and the utilization of SA deflection technology can effectively weaken the reducing atmosphere near the wall.