Abstract: Coal spontaneous combustion fire is one of the major disasters in the process of mine production, which threatens the safety of mine production. Spontaneous combustion of coal is a complex oxidation process, which has to go through different oxidation stages, so it is necessary to set up corresponding indexes to judge different stages of coal-oxygen reaction. The rule of index gas changing with temperature in the process of spontaneous combustion and oxidation of long flame coal was analyzed by temperature programmed-gas chromatography （ＴＧ－ＧＣ）. According to the experimental data of temperature oxidation, spontaneous combustion of coal can be divided into four stages. Using φ（CO）/φ（CO₂） and the third fire coefficient R3 as auxiliary indexes, the stages of coal-oxygen reaction were divided. At the same time, the law of δ18O（ｏｘｙｇｅｎ ｉｓｏｔｏｐｅ） in gas products changing with temperature is obtained by measuring the oxygen isotope abundance in CO and CO₂ of low volume fraction, and the coal spontaneous combustion is divided into four stages according to the law of δ18O.