Abstract: To address the issue of temperature deviations and overheating in the water wall during deep peak shaving of a supercritical coal-fired unit boiler, new safety operation monitoring technology for the water wall was developed. The system employs a B/S architecture, using build thermal load and real-time operating parameters of the boiler as boundary conditions to perform online hydraulic calculations, achieving multi-dimensional monitoring of furnace surface heat load distribution, water wall flow distribution, and fluid state in the water wall loop. Application results show that under a certain deep peaking condition, temperature deviations and overheating occurred in the spiral and vertical water wall of loop 23–25. Based on the monitoring results, the heat load at the front wall elevation from 18 m to 25 m was skewed, leading to water wall overheating. As the unit load decreased, the flame center dropped from an elevation of 38m to 22 m, increasing the cold hopper's heat absorption, which exacerbated the uneven heat absorption of the water wall. By blending low-calorific coal into the bottom mill during the operation of varying load, wall temperature fluctuations were controlled. In another case of wall temperature deviation, the heat load at the front wall elevation around 38 m was excessively high, with the front wall heat absorption ratio abnormally greater than that of the back wall. By adjusting the secondary air volume of the front and back walls, the wall temperature deviation was decreased.