Abstract: Using high temperature gas heating equipment, lignite is heated at different temperatures. The failure forms on the surface were observed by scanning electron microscopy, and the samples were X-ray scanning with high-precision CT. The failure forms were obtained macroscopically and the CT images were processed in binarization to obtain the porosity of lignite and the length and width of cracks in different temperature sections. The results showed that under the action of temperature, thermal stress generated between solid particles of lignite resulted in the pyrolysis of organic matter, which is thermal fracture. The thermal fracture effect is obvious when the temperature is higher than 200 ℃. Below 200 ℃, the evolution of lignite pores and fractures is mainly caused by internal free water and gas loss. After 200 ℃, thermal fracture played a dominant role, and the growth rate of pores and fissures increased greatly, and the porosity increased by 6.83% compared with normal temperature. In the low temperature stage of thermal damage, the destruction of lignite is dominated by long and thin cracks. When the temperature is higher than 200 ℃, the failure form is dominated by irregular ellipses.