Abstract: In order to explore the internal cracks evolution process of high gas and easy self-ignition coal body in low temperature oxidation process, grasp the mechanism of low-temperature oxidation on fissures development of coal, we used nuclear magnetic resonance （ＮＭＲ） technique to detect the evolution process of internal pore size and number of coal in low temperature oxidation process, and used gas chromatography and industrial analysis experiment to analyze the development process of fractured coal. The results show that with the increase of coal oxidation temperature, the pore diameter and the number of coal increased and the porosity increased by 72.2% at 200 ℃ temperature range. Gas chromatography analysis and industrial experiments show that the whole body fracture development is divided into two stages in the process of low temperature oxidation process. In the initial oxidation at low temperature（30 ℃ to 130 ℃）, because of the loss and evaporation of water inside the coal, resulting in the internal microspores expand and connect into the hole; in the late period of low temperature oxidation （130 ℃ to 230 ℃）, because of the macromolecules and volatile oxidation and decomposition in coal body, resulting in internal hole begin to expand and connect into large holes and micro cracks.