TGA, SEM and TEM were used to investigate the variation of PM properties before and after the treatment of direct nonthermal plasma, including the content of elemental carbon and volatile fractions, the surface morphology and the accumulation form of primary particles. The results showed that with the increasing of load, the content of elemental carbon grew and the morphology changed from accumulated clusters to folium piles and then to porous sponge, and the accumulation of primary particles changed from simple fractal block with high thickness into complex fractal stripes. After the treatment of DNTP, the content of elemental carbon grew and the morphology variation versus diesel load was similar to that of before treatment but presented dendrite structure at full load. Accumulation form of primary particles was similar with that of untreated PM obtained at full load, indicating the volatile fractions with high viscosity can be decomposed effectively by DNTP.