O-2/CO2 combustion is a promising technology to facilitate carbon capture in pulverized coal-fired power plants. The reduction of recycled NO, influence of CO2 concentration on the conversion ratio of fuel N to NO, interaction between recycled NO and fuel N, and other factors were experimentally investigated, and correlations were quantitatively obtained. The conversion ratio from fuel N to NO increased with an increasing CO2 concentration in the absence of coal but decreased in the presence of coal. The reduction ratio of NO in the recycled gas depended upon the oxygen/fuel stoichiometric ratio, lambda, and increased with the NO concentration in the recycled gas when lambda = 0.7 and 1.0 but decreased when lambda = 1.2. The conversion ratio from fuel N to NO decreased with an increasing NO concentration in the recycled gas, because of the interaction between fuel N and recycled NO. The global conversion ratio from fuel N to exhausted NO in O-2/CO2 combustion was derived from the experimental results and analysis of the system. The relative importance of different factors in the low conversion ratio from fuel N to exhausted NO in O-2/CO2 combustion has been quantified and found to depend upon lambda. Under all conditions investigated, the reduction of recycled NO was the major factor (over 70%) contributing to the low NO emission in O-2/CO2 combustion.