After the diesel engine works for a long time, dense ash layer will be formed on the diesel particulate filter (DPF) surface, which will increase the back pressure on the DPF surface and seriously affect the normal operation of the DPF. The DPF micro-structure is generated by 3D reconstruction technology. Moreover, the particle layer and ash layer are reconstructed by Quartet Structure Generation Set. The exhaust gas with a velocity of 0.05 m/s~0.25 m/s is introduced into the DPF model. Under the condition of 873 K temperature field, the 3D lattice Boltzmann method is used to explore the influence of the particle layer and ash layer accumulated in its micro-structure on its flow and heat transfer. The results show that with the accumulation of ash, the flow velocity in the DPF increases with the decrease of porosity. The existence of ash layer increases the pressure difference between the inlet and outlet of the structure, and the pressure difference between the inlet and outlet of the structure increases with the increase of the air inlet speed. Under the same flow conditions, the heat transfer process of structures containing ash stratification is faster, and the highest temperature point moves forward accordingly. This has certain guiding significance for exploring the thermal load of ash containing DPF structure.