Staged combustion has been accepted as an effective way to reduce NOx emission. Experimental research is difficult because of the complexity of the chemical reactions related with nitrogen. Based on Miller and Bowman's overall elementary reaction model, NO formation and destruction under fuel staging is calculated in this paper. The accordance of the calculation results with experimental data show that the above model is good for predicting NOx formation and destruction. Sensitivity analysis shows that C, CH, CH2 and HCCO play an important role in NO destruction and reducing under fuel staging. NO generated in the primary zone can be reduced effectively by staged combustion. The main factors that affect NO reducing are the air-fuel ratio in the primary combustion zone, the combustion temperature in the reburning zone and the mass factor of the reburning fuel in the overall fuel. The best air-fuel ratio in the primary combustion zone for NO reducing in the reburning zone is 1. The raising of the temperature in the reburning zone is good for the reducing of NO. The best mass fraction of the reburning fuel in the overall fuel for NO destruction is 30%.