Abstract: Abstract: Particles which contain soluble organic fraction (SOF), soot, and inorganic salt are mainly the result from an incomplete combustion or pyrolysis of fossil fuels and other organic materials. In a diesel engine, the poor mixing of fuel and air creates fuel-rich zones that support particle formation at high temperatures. Numerous studies show that they are harmful to human health when inhaled and may cause cancer. For that reason, it is important to reduce the formation or at least the emission of particles to the environment. Meanwhile, the strict regulations for particulate matter emission have been enforced in many developed countries. A diesel particulate filter (DPF) is currently the dominant diesel particulate emissions control technology to meet stringent air quality standards, however, the oxidation ability of particles is important to the regeneration of the filter bed in DPF. Temperature has a great influence on the oxidation process of particles. Many physical and chemical changes of particles happen at a high temperature, leading to porosity formation of particles during oxidation. The porosity structure of particles is important to the oxidation ability of particles. The micro-orifice uniform deposition impactor (MOUDI) is a favorable apparatus for obtaining the particle size distribution and collecting the particles in different size ranges after classification. Thermogravimetric analysis (TGA) has been widely used as an analytical method for investigating the relationship between the material weight and temperature under the condition of programming a temperature rise. The curve of the sample weight then can be obtained with the temperature. A derivative thermal gravimetry (DTG) curve, the first order differential to a TG curve, can reveal the features of mass variation with the temperature. Small-angle X-ray scattering (SAXS) is a widely used diffraction method for studying the structure of the sample. In this study, the micro-orifice uniform deposit impactor was used to collect particle samples; the thermal gravimetric analysis was used to investigate the ignition of particles as a basis for determining the oxidation temperature; and the change rules of porosity structure parameters, porosity quantities, and size distribution of particles in the oxidation process were investigated by synchrotron (SAXS). The results of the thermogravimetric analysis showed that the ignition temperature of diesel particles was 487℃, and the oxidation temperature range should be set up under 400℃ for study on the porosity structure of particles during oxidation. The results of small-angle X-ray scattering showed that the electron density difference of combustion particles increased, and the size of particles reduced the fractal dimension, average radius, gyration radius, and axial length all significantly increased as the oxidation temperature increased. The tightness of the porosity structure decreased, and the number and size of porosity all increased with increasing oxidation temperature. The porosity size of particles at 100℃ was mainly distributed in a range of 6-7 nm. The porosity size of particles at 200℃ was mainly distributed in a range of 8-9nm. The porosity size of particles at 400℃ was mainly distributed in a range of 12-13 nm.The study provided valuable information on mechanisms of particle oxidation.