Abstract: In order to explore the micro structure variation features of coal after pre-oxidation, the liquid nitrogen adsorption experiment was adopted to measure the specific surface area and pore structure of Liujia lignite, Sitai lignite, Tongxin bituminous coal and Baijigou anthracite, the variation laws of specific surface area, pore size distribution and pore volume with coal sample pre-oxidation temperature and pre-oxidation time were obtained. The results show that the specific surface area of oxidized coal samples from different coal mines has the same change law: pre-oxidized coal samples at 50 ℃>original coal samples >pre-oxidized coal samples at 120 ℃> pre-oxidized coal samples at 200 ℃, and the longer the pre-oxidized time is, the smaller the specific surface area will be. The pore size of pre-oxidized coal samples from four coal mines is concentrated in the range of 2-10 nm. Coal samples 50-6(pre-oxidized at 50 ℃ for 6 h) have the highest cumulative pore volume value, while coal samples 200-24(pre-oxidized at 200 ℃ for 24 h) have the lowest cumulative pore volume final value. The internal pore network of coal sample 50-6 is the most developed, it is easier to react with oxygen under the same conditions, thus has the highest spontaneous combustion risk, while the coal sample 200-24, on the contrary, has the lowest spontaneous combustion risk.