To reduce particulate matters (PM) in diesel exhaust gas, stricter exhaust emission standards such as Euro V are being set in many countries Recently, for the after-treatment of exhaust gas, a diesel particulate filter (DPF) has been developed. Latest researches have shown that DPF filtration efficiency can be as high as 99%. However, the filter would be plugged with particles to cause an increase of filter back-pressure, which must be kept at lower levels, because the higher back-pressure increases fuel consumption and reduces available torque. Here, we are focusing on NO(x)-soot conversion system. There are two stages for PM oxidation. At the first step, the catalyst oxidizes NO in exhaust gas into NO(2) At the next step, NO(2) reacts with soot to produce CO and CO(2) However, the reaction rate and quantitative effect of NO(2) on soot oxidation is not clear, because it is difficult to observe small-scale phenomena in DPF experimentally, and there is not enough information on the PM oxidation In this study, we simulated the above two-stage system In the first part, the reaction with Pt catalyst for the oxidation of NO to NO(2) was simulated in non-porous flow-through filter. The catalytic reaction mechanism was discussed. In the second part, we simulated the flow in wall-flow filter to confirm the effectiveness of regeneration process by NO(2) in the real cordierite DPF (C) 2010 Elsevier B.V All rights reserved