Co-combustion of sludge and other fuels such as coal in the circulating fluidized bed (CFB) boiler is an effective way to reduce,harmless and resource sludge treatment. To understand the influence of sludge co-combustion on the material balance and operation performance of a large-scale CFB boiler,taking a 330 MWe subcritical CFB boiler as the research object,the material balance characteristics after sludge mixed combustion were predicted and analyzed with the help of one-dimensional CFB mathematical model. Then,the boiler operation performance under co-combustion condition was analyzed in combination with some field test data. Model calculation results show that in the mixed fuel of raw coal gangue and coal slime (the mass fraction of coal slime is 15%),if 10% mass fraction of sludge is added by replacing part of the coal gangue,the particle size of fly ash and bottom ash will change little,while the circulating ash size may be slightly increased. Meanwhile,the solid circulation rate will increase by nearly 30%,from 9.2 kg/(m2·s) to 11.8 kg/(m2·s),the average pressure drop across dilute phase zone as well as the particle suspension density will increase by about 35%,and the share of fly ash in the total discharging ash will increase by about 1.5 percentage points. Besides,the residence time of solid particles inside furnace can also be extended. In addition,the field test results under different boiler loads (from 50% to 100% load) reveal that when 10% mass fraction of sludge is mixed in the feeding fuel,the bed temperature has dropped by about 10 ℃,the exhaust gas temperature has raised within 3 ℃. The steam temperatures at the outlet of primary superheater and primary reheater have increased,while the temperature [JP2rise is within 10 ℃ at most boiler loads,and the outlet steam temperature of in-furnace platen superheater has slightly decreased by 2-15 ℃. The results in this paper indicate that the co-combustion of sludge with coal is beneficial to improving the solid circulation performance of the CFB boiler to some extent,moreover,the convection heat transfer in tail flue may be enhanced,while the heat transfer coefficient of the platen heating surfaces in furnace may decrease. However,on the whole,for the wide load range,if the blending ratio of sludge in the mixed fuel is not high,the changes of boiler steam parameters are small,which has little impact on the overall operation performance.