Abstract: Diesel particulate is one of the main sources of atmospheric particulate matter PM2.5, which seriously harms human health. With the emission regulations become increasingly stringent, higher requirements have been put forward, not only on the quality of particulate emissions but also on the particle number. The change trend of particle size distribution and oxidation characteristics of the diesel particulate are analyzed, in order to understand the change process of the diesel engine particles in the exhaust pipe. For further reduction of the diesel engine exhaust particulate, the post processing technologies have been widely used, such as diesel particulate filter(DPF). A lot of carbon dioxide(CO₂), water vapor, hydrocarbon(HC) and particulate matter and other components are contained in the diesel engine exhaust, and the temperature, pressure and other parameters of the exhaust gas flow changed in the exhaust pipe of the diesel engine. The exhaust particulate matter was also accompanied by condensation and oxidation reduction and other physical and chemical processes, and as a result the physical and chemical characteristics of particles also changed. The particle size distribution and oxidation characteristics of the particles were important for the particle capture efficiency and regeneration. The particle size distribution along the direction of movement of the exhaust gas flow and different positions was measured by using the engine exhaust particle size spectrometer(EEPS). Along the direction of the exhaust gas particles at different sites during the pyrolysis process, pyrolysis kinetic parameters, ignition temperature and burnout characteristics index were studied, and particle pyrolysis reaction rate and degree of difficulty were analyzed by using the device of thermogravimetry/differential simultaneous thermal analyzer. According to the experiment data, along the direction of the exhaust gas flow, the number of nucleation particles decreased, the number of aggregated particles increased, and the particle size of aggregated particles became larger. It showed that in SOF(soluble organic fraction) evaporation stage and soot oxidation process, the particle weight loss rate increased, and the weight loss peak temperature decreased; along with the diesel engine exhaust gas flow direction, when reducing the temperature of the gas, the content of H₂O in particles increased from 1.3% to 2.46%, the content of SOF increased from 38.21% to 42.05%, the soot percent content decreased from 57.84% to 52.24%, and the ash content increased from 3.01% to 3.25%; the pre-exponential factor of particle was reduced from 7.93×10¹² to 4.67×10¹² and the activation energy could be reduced from 157.3 to 127.9, the ignition temperature decreased from 546 to 501 ℃, which was reduced by about 8.2%, the combustion characteristic index increased from 8.16×10^-9 to 1.62×10^-8, and the burnout characteristics index was risen by 14.5%. Therefore, based on the study of the particle size distribution and oxidation characteristics which came from the small non-road diesel engine exhaust pipe of particles, it can be concluded that along the exhaust gas flow direction, with lower exhaust temperature, the burnout performance of the particle gets improved and effectively raises the regeneration of particle collector.