In order to study the index gas in the process of coal spontaneous combustion and cooling, the experimental coal sample was heated by coal spontaneous combustion and fire extinguishing simulation test system, and the oxygen sample was naturally cooled to reduce the temperature of the coal sample. The coal sample cooling was divided into three temperature segments, the temperature coefficient and gray correlation degree were calculated and compared by different indexes. It was found that the correlation analysis and gray correlation analysis of the index gas and temperature in the coal sample cooling process showed good correspondence. During the cooling process of coal sample, the Beston coefficient should be used as the main index in the temperature range of 400～230 ℃ and 80～30 ℃. In the temperature range of 230～80 °C, the ratio of carbon oxide should be taken as the main index  to judge the status of the fire zone.