Abstract: The overall layout of supercritical boilers is primarily divided into Π-type and tower-type configurations. Due to issues such as flue gas turning, easy ash deposition in the rear flue, and higher steam pressure losses in the heating surface of Π-type boilers, tower-type boilers have gradually been developed. Currently, tower-type boilers typically adopt the tangential combustion method, while opposed combustion offers advantages such as relatively stable combustion, easier slagging control, and more uniform upward airflow. To thoroughly investigate the within characteristics of opposed firing and tangential firing tower boilers, numerical simulation methods were employed to study a 660 MW ultra-supercritical single-reheat opposed firing tower boiler and a 660 MW ultra-supercritical double-reheat tangential firing tower boiler. The results showed that the overall distribution trends of CO and O₂ the furnaces of both boilers were similar. A large amount of NO was generated in the primary combustion zone, while the NO concentration decreased in the burnout zone. In the tangential firing boiler, the flue gas deviation in the heating surface area was significant. The temperature unevenness coefficient in the superheater region of the tangential firing boiler was notably higher than that of the opposed combustion boiler, with a maximum value of 1.456. However, the temperature unevenness coefficient in the high-temperature reheater region was lower than that of the opposed combustion boiler. In the superheater and high-temperature reheater regions, the velocity unevenness coefficient gradually increased for both types of boilers. Moreover, the unevenness index of the tangential firing boiler was always higher than that of the opposed firing boiler. Additionally, in the superheater and high-temperature reheater regions, the heat load unevenness coefficient of the tangential firing boiler was consistently higher than that of the opposed combustion boiler. The high-temperature corrosion ratios on the side walls of the opposed firing boiler and the tangential boiler were 36.59% and 85.04%, respectively. The maximum heat load deviation coefficients of the water wall were 2.64 for the opposed firing boiler and 2.02 for the tangential firing boiler. Opposed firing tower boiler and tangential firing tower boiler each have their own advantages in terms of uniform flue gas temperature distribution, reducing high-temperature corrosion on side walls, and uniform heat load on water walls. Opposed firing tower boiler exhibits smaller flue gas temperature deviations in the heating surface area and a lower proportion of high-temperature corrosion on side walls, while tangential firing tower boiler has smaller heat load deviations on the water walls.