Abstract: To complete grading warning of spontaneous combustion for the fully mechanized top-coal caving face, the primary mineable No.3 coal seam is taken as the research object. Through temperature-programmed experiment, site test and statistical analysis, the spontaneous combustion mark gas of coal mine is optimized and the critical value of CO index in goaf, return corner and return air of working face is determined. Based on this, a composite index warning system of spontaneous combustion of working face is established. The results show that the critical values of CO concentration in goaf, return corner and return airflow are 242×10^-6, 59.6×10^-6 and 20×10^-6 respectively. Responses for four levels warning, green (I), blue (II), orange (III) and red (IV) ,were set up in all regions.