When predicting the variation of pore structure during O-2/CO2 combustion of coal chars using the random pore model (RPM), it is impossible to calculate exactly the structure parameter psi from the pore characteristics. The values of structure parameter psi, which were calculated based on its fractal feature at various carbon conversions, should be almost constant. However, this investigation exhibited a drastic increase of psi at the end of combustion reaction. In this work, structure parameter psi of the RPM was modified according to the experimental analysis and a new model, fractal random pore model (FRPM), was constructed. Compared with other models such as RPM, discrete random pore model (DRPM), the Struis model (Model I) and the Liu model (Model II), it was found that fractal random pore model was more accurate to describe coal chars combustion, especially at higher conversions. Using the FRPM, O-2/CO2 isotherm combustion of coal chars were analyzed at different temperatures. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.