Diesel Particulate Filter (DPF) is widely used to trap Particulate Matter (PM), which is one of the atmospheric pollutants. PM oxidation catalyst increases the efficiency to oxidize PM. The catalyst can keep the efficiency in contact with PM layer. So, when PM layer is detached from the catalyst surface or ash prevents contact between catalyst and PM, the efficiency deteriorates. In this report the movement of PM layer and ash layer was visualized in Ag₂SO₄/Al₂O₃ coated DPF during the regeneration. The authors showed the regeneration method to remove both detached PM and ash to keep PM oxidation efficiency.