The effects of biomass types (including cotton stalk, wheat straw, rice husk, and rice straw), the stoichiometric ratio in the reburning-zone (SR2), the reaction temperature in the reburning-zone (t(2)), the particle sizes of biomass rebuming fuels and the rebuming fuel fraction (R-ff) on NO reduction efficiency during biomass rebuming were investigated systematically in an entrained flow reactor. The NO heterogeneous reduction mechanism resulting from the reburning of wheat straw and its char was analyzed. The results indicated that cotton stalk has the best performance of NO reduction, wheat straw is in second place, and rice husk and rice straw are less effective. In the range of t(2) = 900-1100 degrees C NO reduction efficiency increases when the reburning-zone reaction temperature is increased at the same SR2. NO reduction efficiency increases insignificantly with a decrease in the particle size of the biomass with d(p), < 425 mu m. NO reduction efficiency follows a pattern of first increasing and then decreasing with the decreasing of the SR2 or the increasing of the R-ff. The higher NO reduction efficiency (more than 50%) can be achieved in the range of SR2 = 0.7-0.8 or R-ff = 20-25% during reburning with the four types of biomass. The contribution of NO heterogeneous reduction by wheat straw char to the total NO reduction was in the higher range of 59-68%, whereas the R-ff was in the range of 10-26%.