Abstract: In order to study the factors of gas combustion (explosion) in goaf induced by hard and thick sandstone roof containing pyrite, the goaf of 121109 working face in Xinji No.2 Coal Mine was studied by means of field monitoring, laboratory test and theoretical analysis. The results show that the roof sandstone of 11-2 Coal seam is grey-white, fine-grained structure, massive structure, and the content of CaO and Fe2O3 is high. According to the calculation formula of the collision velocity of roof sandstone collapse collision, the theoretical value of the interval of the collision velocity of roof sandstone collapse is 2.78~8.31 m/s and the coefficient of affluence is 3.34~9.97 m/s, and the continuous spark will occur when the sandstone roof rubs at very low velocity (the test contact line velocity is 0.3 m/s), and under the same contact friction condition, yellow iron will be produced. It is easier for ore cores to produce continuous sparks, and the spark intensity is higher than that of pure sandstone cores.