Abstract: The influence of calcium-based particles on the selective non-catalytic reduction (SNCR) process was investigated in a drop tube furnace reactor; the tests under different temperatures (600~1 100 ℃), normalized stoichiometric ratio (NSR) of NH₃/NO (0.5~2.0) and O₂ concentrations (0.5%~5.0%), with ammonia and urea as reducing agents, were considered. The results showed that the raw material, CaCO₃ and CaO have inhibitive effect on the SNCR performance; the extent of this effect is significant at low temperature but attenuates with the increase of temperature. Raw material exhibits the strongest inhibitive effect on the SNCR at low temperature because of the catalytic activity of impurity in the raw materials, while CaO has the strongest effect at high temperature. The efficiency of SNCR is increased by increasing NSR, while the effect of calcium-based particles on SNCR remains unchanged. The optimal O₂ concentrations for NO_x removal is 1% with raw material and 2% with CaCO₃ and CaO. The SNCR performance in the presence of calcium-based particles is characterized by the competition of denitration reactions between gaseous de-NO_x and the particle-catalyzed oxidation of reductant.