Abstract: The water wall temperature of large utility boilers with sub-critical and above parameters is generally high.The application of low NO_x staged combustion technology leads to the oxygen deficiency in the primary combustion zone,which often causes serious high temperature corrosion.The sample of the water wall tube after high temperature corrosion was cut off from a 300 MW utility boiler for characterization analysis.The cause and the classification of high temperature corrosion were discussed. The results show that the corrosion products contain a large amount of FeS,which belongs to typical sulfide corrosion.Blue and yellow-green products are covered on the tube surface,whose main composition are iron oxides and sulfides.The iron sulphides in the blue products are FeS while in yellow-green products are ZnS.The FeS presents a hexagonal crystal and with a size of 10-20 μm.Meanwhile,large amount of unburned fly ash particles were found at the surface of the sample tube,indicating that the air distribution in the furnace were irrational and the flame brushing walls phenomenon was existent.After the reconstruction of the burners,the cold aerodynamic field using fireworks in furnace was conducted.It is found that the whole tangential circle is in good condition and does not deviate from the geometric center of the furnace,which meets the design requirements.The diameter of imaginary primary air tangential circle is 790 mm,which basically coincides with the design value.The air flow in each layer is relatively stretched,and no obvious brushing walls phenomenon is observed.The imaged flame is full of the furnace and the condition of the aerodynamic field is obviously improved.The hot state operating results show that the adaptability to coal change is greatly improved,the combustion stability and anti-slagging ability are greatly improved.The boiler can be continuous operated above 800 t/h load under 50% blending ratio of lean coal.The flame colour is uniform and no large continuous coking phenomenon was found.The high temperature corrosion was obviously relieved.