The micron expanded graphite is prepared by the method of chemical oxidation. Sulfuric acid and ice acetic acid are used as inserting reagent, potassium dichromate is used as an oxidizing agent. The optimum mass ratio is as follows: mC: mH2SO4:mCH3COOH:mK2CrO7=1:5:3:0.5. The reaction time is 60 min and the temperature is at room temperature. The measured result of FTIR, SEM and Laser Particle Size Analyzer show that target product is successfully prepared. Its expanded volume is up to 8.0mlg-1. At the same time, the static and dynamic infrared extinction properties of micron expanded graphite are measured. Results show that the micron expanded graphite has stronger Infrared extinction ability than the raw graphite. The cause is that the surface of micron expanded graphite has some open or semi-open small holes which can obviously absorb infrared radiation.