Abstract: In order to research spontaneous combustion and oxidation characteristics of coal gangue from micro level, free radical variation law in spontaneous combustion and oxidation process of coal gangue were analyzed by using experimental system for free radical determination of coal gangue. The results show that with the increase of temperature, free radical concentration increases slowly and then increases rapidly, g factor decreases slowly and then increases rapidly and then decreases, and CO production quantity increases slowly and then increases rapidly. The higher the sulfur content is, the lower the critical temperature for coal gangue from slow oxidation to rapid oxidation and the temperature required for rapid growth of g factor is, and the greater the CO production quantity is. It can be seen that sulfur content promotes spontaneous combustion of coal gangue, so desulfurization treatment should be carried out before accumulation of coal gangue.