Abstract: The paper analyzed “12-5”gas explosion disaster of Ruizhiyuan Coal Industry Co., Ltd. which causes 105 deaths, and got conclusions: the explosion time was 2007-12-05T23:07; gas explosion source located at 40 m digging face of No.9 coal seam; 40 m digging face was excavated without wind, which resulted in gas concentration accumulating to explosive concentration limits; the flame produced by shotfiring at 40 m digging face detonated gas and coal dust involved in the explosion; the No.9 coal seam of the mine had no safety monitoring system and the gas gauge could not be found to cut off power and withdraw in time; the mine was confused in electromechanical management, for example, it did not use explosion-proof junction box to connect cables, extensively used non-explosion proof tricycles, and did not use integrated security devices to protect coal drill.