In order to investigate the evolution law of structure and chemical components of diesel engine particulates during passing through diesel oxidation catalyst (DOC) and diesel particulate filter (DPF), particulates samples emitted from an electronic control high pressure common rail, turbocharged, inter-cooler diesel engine with exhaust after-treatment device were collected on the glass fiber filters. Raman spectrums at different points were measured, and characterizations of the spectrums were compared. The results showed that the Raman spectrum of engine particulates was composed of five peaks and the Raman shift of the peaks changed within a very small range. Every characterization parameter describing the structure and components of particulates varied with the different measuring points, i. e. as the measuring point shifted backward, the ID1 /IG decreased, ID2 /IG increased, ID3 /IG ,ID4 /IG and IALL /IG had the trend of first increase and then decrease, which indicated that the changing process of structure and components of the particulates was not only a physical process but also a chemical one. On behalf of the degree of graphitization of the particulates of ID1 /IG increased with the backward shift of the measuring point, but the organic fractions in the particulates reached maximum.