Abstract: NO reduction through coal reburning can be conducted in two ways: homogeneous reduction by volatile matters and heterogeneous reduction by char. Experiments were undertaken in a 1D entrained flow reactor (EFR). The effects of the ignition including volatile homogeneous ignition (GI) and carbon heterogeneous ignition (HI) on the reburning process were studied. The results indicate that with increasing the concentration of O2, GI occurs and NO reduction efficiency decreases sharply. At the beginning of HI, the reduction efficiency increases in a narrow span of lower O2 concentration, and with the O2 concentration increasing the reduction efficiency will fall due to the overmuch oxygen. Higher reburning zone temperature can promote NO reduction reactions but also improve the ignition reaction under lower O2 condition. The effect of particle sizes on coal ignition and NO reduction process is more complicated. When the coal size is greater than 40μm, the reduction efficiency will decrease with the particle size increasing.