Abstract: An experimental test was carried out to study the NOx reduction efficiency using ammonia injection SNCR (selective non-catalytic reduction) technology. Chemical kinetics modeling was investigated simultaneously. Results show that higher temperature causes oxidization of ammonia while lower temperature decreases reduction efficiency. The optimal temperature range is about 850 ℃ to 1 100 ℃ in our test, highest NOx reduction about 82% is achieved. With the increasing of ammonia dosage chemical reaction slows especially at lower temperature. The time reaching chemical equilibrium dramatically increases when temperature is lower than 700 ℃. Therefore, the acceptable temperature with short time in the coal-fired boiler should be higher than 700 ℃. The risk of ammonia leakage is neglectable when temperature is higher than 950 ℃. It plays a key role in the whole reactions that competition between two chain-branching reactions of NH2. Lower temperature is beneficial for the first chain-branching reactions which are the DeNOx process, while the higher temperature is beneficial for the second chain-branching reactions which are the ammonia oxidization process. The homogeneous numerical simulation results show good agreement with the experimental data especially at higher temperature.