Abstract: Aiming at the problem of uneven combustion in a 1 000-MW ultra supercritical boiler, the in-depth combustion optimization tests are conducted, including combustion air distribution optimization, primary air volume optimization, coal powder fineness adjustment and total combustion air distribution adjustment. Through the tests, the optimal operation curve is obtained. The combustion test under different load conditions exhibits that after the combustion optimization, the fan power consumption, the NOx emissions as well as the heat losses of exhaust flue gas and unburned carbon are all reduced. Hence the boiler efficiency is improved and the effectiveness of the combustion optimization is verified.