Abstract: To address the high-temperature corrosion of waterwalls in a 1000 MW opposed-firing boiler, a multi-annular wall-air nozzle with wall-directed outlets and a corresponding spatially optimized arrangement were proposed and implemented in the field. A pulverized-coal combustion model was coupled with an organic sulfur evolution model and a pyrite particle deposition model to analyze the tendency of waterwall high-temperature corrosion before and after the retrofit from the perspectives of gaseous sulfur species and sulfur-containing particle deposition. The results showed that the simulated values agreed well with the field measurements. The burner jets partially deflected toward the sidewalls after colliding in the furnace center, promoting the transport of H₂S and pyrite particles to the near-wall region and forming high-corrosion-risk zones characterized by both H₂S enrichment and particle deposition. The wall-air system formed a continuous air layer along the waterwall, which increased the near-wall O₂ concentration and promoted H₂S oxidation, reducing the peak average H₂S concentration by approximately 70%. Meanwhile, the wall air altered the trajectories of pyrite particles in the near-wall region and reduced their deposition probability. The proposed scheme can therefore mitigate waterwall high-temperature corrosion through the synergistic reduction of near-wall H₂S concentration and pyrite particle deposition rate.