Abstract: In view of the high leakage intensity in the goaf and the difficulty of preventing the hidden danger of spontaneous combustion in the three dimensional goaf, the natural ignition causes are analyzed based on the FTA analysis method. Based on the long-term field record, the probability and weight of the basic events and the intermediate events are determined, and the structural importance, probability importance and critical importance of the respective ignition causes in natural fire accidents are calculated. It makes the natural fire prevention work more pertinent, and makes the limited manpower and material resources play the most important role in the internal cause of the fire prevention and control.