Abstract: Through the analysis of easily spontaneous combustion reasons at gob of the fully mechanized caving face in Gengcun mine No.Ⅱ₃ seam.The paper gets the CO emission laws of fully mechanized caving face,constructs the fire extinguishing and prevention technology system,and determines that the critical value of index gas CO concentration is 100×10^-6in gob of the fully mechanized caving face,which ensures safety advance of working face and provides reference to the similar mine.