Particulate matter (PM) including soot in diesel exhaust gas is a serious atmospheric pollutant, and stricter exhaust emission standards are being set in many countries. As one of the key technologies, a diesel particulate filter (DPF) for PM trap in the after-treatment of the exhaust gas has been developed. Typically, the inlet size of filter monolith is about 2 mm, and the thickness of the filter wall is only 0.2 mm, where soot particles are removed. It is impossible to observe the small-scale phenomena inside the filter, experimentally. Then, in the present study, we conducted microfluidic simulation with soot oxidation.Here, a real cordierite filter was used in the simulation. The inner structure of the filter was scanned by a 3D X-ray CT Computed Tomography) technique. The advantage is that it is non-intrusive system, and it has a high spatial resolution in the micrometer. By conducting tomography-assisted simulation, we obtained local velocity and pressure distributions of the complex microfluidics in the filter, which is hardly obtained by measurements. Especially, the conjugate simulation of gas-solid flow was presented. That is, to consider the heat transfer to the solid wall of the filter substrate, the equation of heat conduction was solved, simultaneously. Based on the temperature change and reaction rate in DPF, the conditions for the after-treatment were discussed.