Abstract: The large-scale grid connection of new energy sources poses significant challenges to the stability of new power systems. The state has proposed new flexibility indicators for coal-fired power plants, requiring them to play a crucial role as a stabiliser and regulator. To address the current challenges faced by coal-fired power plants, such as difficulty in maintaining stable combustion at ultra-low loads and delayed response to load changes, a solution involving adjustable coal powder burners with a stable combustion structure has been proposed. This solution was tested on a 300 kWth hot-state test platform to compare combustion characteristics under different load conditions, with the aim of studying the low-load stable combustion performance and rapid load response capability of the adjustable coal powder burners. Test results indicate that the displacement of the primary air duct nozzle at the tail end significantly affects combustion performance at low loads. By altering the relative position of the coal powder outlet to influence the effective volume of the stable combustion chamber, the flame shape is improved, effectively enhancing the low-load stable combustion performance and rapid load-changing capability of the coal powder burner. At 20% load operation, shifting the primary air duct nozzle 10 mm to the right caused the temperature at the measurement point to increase rapidly by 5.6%, significantly improving the coal powder ignition characteristics and the mixing degree of primary and secondary air, thereby enhancing combustion stability and combustion efficiency. At 15% and 20% load, the carbon content in fly ash was 1.83% and 1.34%, respectively, corresponding to combustion efficiencies of 97.76% and 98.36%. The maximum NOx emissions (calculated at 6% O2) were 429 mg/m3 and 318 mg/m3, respectively, verifying the low NOx emission performance of the adjustable coal powder burner with a stable combustion structure. The lower limit of stable combustion at 20% load was surpassed, achieving stable combustion at 15% load and basic stable combustion at 10% load. The load change rate reached 6%/min, with the maximum carbon content in fly ash being 2.04%. In rapid load change dynamic response tests, the adjustable coal powder burner with a stable combustion structure maintained good combustion efficiency and stability, verifying its excellent performance in rapid, deep, and flexible peak shaving processes.