Nonthermal plasma (NTP) technology can oxidize and decompose diesel particulate matter (PM) under much lower temperatures (<= 200 degrees C), showing promise for potential applications. A test bench for the treatment of diesel PM using an NTP injection system was constructed, and PM samples before and after NTP reaction were accumulated on filter papers. The apparent morphology, oxidative activity, surface functional groups, and soluble organic fractions (SOF) components of PM samples were investigated using modern techniques (i.e., SEM, TGA, FT-IR, and GC-MS). Results show that after NTP reactions, the amount of PM declined substantially and the surface stacking structure became relatively smooth; the proportion of SOF reduced and that of DS increased. Carbon atoms and functional groups on the edge or surface of the carbon layer were first oxidized by the NTP active substance (O-3, O) to form CO or CO2, causing carbon atoms to fall off the original bond and new oxygen-containing functional groups to be generated as intermediates. After the NTP reaction, the oxidation characteristic temperatures decreased and high-carbon-atom-number components were transformed into low-carbon-atom-number components. Results reveal that NTP can improve PM oxidizing activity and promote low-temperature combustion of PM; PM decomposition can be regarded as a process of constantly removing carbon atoms.