With focus on investigating the effect of combustor scale on the conversion of fuel-N to NOx and N2O, experiments are carried out in three combustors, including single coal particle combustion test rig, laboratory scale circulating fluidized-bed boiler (CFB) and full scale CFB in this work. For single coal particle combustion, the majority of fuel-N (65%-82%) is released as NOx, while only a little (less than 8%) fuel-N yields N2O. But in laboratory scale CFB, the conversion of fuel-N to N2O is increases, but the conversion of fuel-N to NOx is quite less than that of single coal particle combustion. This is because much char in CFB can promote the NOx reduction by increasing N2O formation. In full scale CFB, both of the conversion of fuel-N to NOx and the conversion of fuel-N to N2O are smaller than laboratory scale CFB.