Based on diesel engine bench test， a DOC device was added on a diesel engine to analyze the particle number concentration and the variation trend of both SOF content and activation energy of particles before and after the DOC device. Results show that the DOC device can reduce the nucleation mode particle number concentration and the accumulation mode particle number concentration， but with the increase of torque， the DOC device will increase the accumulation mode particle number concentration. The effect of DOC on the total particle number concentration shows a trend of decreasing first and then increasing with the increase of torque. The DOC device can reduce the content of SOF component and increase the apparent oxidation activation energy of particles under the conditions of torque of 50 N·m and 100 N·m. In addition， the apparent oxidation activation energy of exhaust particles shows a decreasing trend as a whole with the increase of SOF content.