The characteristics of ash deposition in the wall-flow filter with active regeneration were analyzed, and a computational model of wall-flow diesel particulate filter for ash deep-bed deposition process was proposed. Based on the mathematical model, the effect of ash deposition on the flow resistance of filters was studied, and the accuracy of mathematical model was verified by the experimental data. The results showed that the flow resistance of filters increased quickly with the ash depth deposition. The flow resistance incrensed linearly at the beginning of the ash cake filtration phase, but the increase accelerated when the ash deposition amount exceed 15 g/L. The ash layer had a more significant influence on filter pressure drop than ash end-plugs. This study reveals some characteristics of ash depth deposition process, and is helpful for enhancing the durability of diesel particulate filter.