Four-wall tangential firing (FWTF) is a newly developed furnace arrangement used in supercritical and ultra-supercritical 600-MW boilers. In this study, flow characteristics of the flue gas in furnace of a 660-MW boiler firing pulverized coal with FWTF arrangement were investigated through numerical simulations. The variation characteristics of the tangential circle size of the furnace and flue gas bias at the furnace exit were determined. The results show some differences in the flue gas characteristics between the FWTF and traditional four-corner tangential firing (FCTF) in the furnace. In the FWTF, the variation in the actual sizes of the tangential circle in the burner zone is insignificant; the maximum size with respect to geometric limitations is largely maintained. Hence, unlike conventional FCTF, the size of the tangential circle cannot be used as a reliable parameter to analyze the variation in flue gas characteristics in the FWTF. Moreover, the flue gases are uniform and have high filling factors in the furnace. The simulation results show that, in the FWTF, the residual rotational momentum near the furnace exit is significant, thereby leading to variations in the flow and temperature on both sides of the furnace exit. This behavior is similar to that observed in the FCTF, which requires sufficient attention.