Pulverized coal combustion technology in O 2 /CO 2 atmosphere is widely accepted as a new combustion technology. This method does not only recycle CO 2 , but also lowers NO x emission. However, pulverized coal combustion technology has several problems such as pulverized coal ignition delay, low flame temperature, and incomplete burning. Such issues have attracted the attention of the local and international academic communities. This study adopts a numerical simulation to analyze the combustion characteristics of conventional sized pulverized coal (70μm) mixed with superfine pulverized coal (20μm) in O 2 /CO 2 atmosphere. The influences of co-combustion of two sizes pulverized coal on ignition, combustion flame structure, and NO x generation were analyzed. Results showed that the co-combustion of superfine and conventional-sized pulverized coal can enhance the ignition and combustion performance of pulverized coal in O 2 /CO 2 atmosphere. The improved ratio of superfine pulverized coal promotes ignition process of pulverized coal and combustion intensity. Moreover, co-combustion can decrease NO x generation. As the ratio of superfine to conventional sized pulverized coal increases, NO x emission decreases. The reduction effect of NO x is most significant when the ratio of superfine to conventional sized pulverized coal increases from 30% to 50% and the co-combustion of superfine and conventional sized pulverized coal in O 2 /CO 2 atmosphere can simultaneously improve combustion performance and reduce NO x discharge.