The O-2/CO2 combustion of coal chars currently considered as one of the promising technologies has a remarkable effect on reducing greenhouse gas emissions, and it is of importance to investigate the mathematical model of pore evolution at char reaction process, while discrete random pore model (DRPM) can be usually considered as the mathematic modeling of pore evolution for effective prediction of char combustion at O-2/CO2. In this work, pore structure variation of three chars during reaction at O-2/CO2 were presented by the N-2 isothermal adsorption/desorption method. The universally used assumption of proportional relation of superficial area and combustion rate was improved for application to coal chars, indicating true superficial area associated with the reaction rate should be corresponding to the pore superficial area 2 pi l(r(0) + theta Delta r/2). Therefore, a new pore structure model (MDRPM) was created to simulate carbon conversion of three coals combustion process in O-2/CO2 when chemical reaction is considered. Compared with the Liu model, the Struis model, as well as the Bhatia model (DRPM), carbon conversion calculated by the MDRPM was more consistent to experimental values for three char reaction process. According to these models, the combustion characteristic of coal chars in O-2/CO2 was investigated.