Abstract: In order to improve the predicting and forecasting accuracy of spontaneous combustion of 4^-2 coal seam in Chaijiagou Mine, this experiment simulates the spontaneous combustion process of 4^-2 coal seam with XK -Ⅶ large-scale coal spontaneous combustion test bench. The spontaneous combustion characteristic parameters, single index gas and compound index gas have been analyzed. The results of the experiment show that when coal temperature is 70 ℃ to 80 ℃, the oxygen consumption rate of sample coal accelerates obviously and the slope of exothermic intensity curve gradually increases; when coal temperature is 100 ℃ to 120 ℃, the oxygen consumption rate of sample coal increases intensely and the slope of exothermic intensity curve increases obviously. In such case, it’s assumed that the critical temperature of spontaneous combustion of 4^-2 coal seam is 68 ℃ to 80 ℃ and the dry cracking temperature is 100 ℃ to 120 ℃. Because φ(CO), φ(O₂)/φ(CO+CO₂) varied with coal temperature with great flexibility and regularity and they are easy to be detected under the mine,φ(CO), φ(O₂)/φ(CO+CO₂) are selected as the primary index gases to predict the spontaneous combustion of 4-2 coal seam; because φ(CH₄)/φ(C₂H₆), φ(C₂H₄)/φ(C₂H₆) can reflect the development stage of spontaneous combustion of 4^-2 coal seam to some extent, φ(C₂H₄), φ(CH₄)/φ(C₂H₆), φ(C₂H₄)/φ(C₂H₆) are selected as the auxiliary index gases to predict the spontaneous combustion of 4^-2 coal seam.