The oxidation and pyrolysis experiment were conducted to detemune the gas composition of coal samples in the 14252 fully echanized caving face of the Xiaotun mine，Fengfeng mining area. The air of the goof was collected with the gas sampling system specially made, and detemvned to divide the range of spontaneous combustion three canes. The results show that the C₂H₂ could well serve the prediction index of spontaneous combustion; and the three canes are divided as follows: the range of heat dissipation belt is 0-30m, the spontaneous combustion belt 30-127m, and the asphyxia belt over 127m.