Abstract: Due to the motion of flying gangue is complicated,dynamic and uncertain in the working face of steep seam mining,accurate assessment the threat level of flying gangue to people or equipment is the basis of flying gangue protective design in steep seam mining.Based on the geological conditions and characteristics of strata behaviors of No.25221 working face in 2130 Coal Mine,Based on the damage degree of flying gangue to people or equipment,three dynamic variables of flying gangue,namely the velocity,angular velocity and the distance from the people or equipment in the lower ends of the working face were chosen as the basis for evaluating the threat of flying gangue to people or equipment,the dynamic bayesian network model was constructed by combining expert knowledge with the historical measured data of flying gangue on the working face,and the dynamic observation nodes were selected according to the viterbi algorithm,the probability of dynamic threat level of flying gangue moving along the working face was obtained.The results show that with the increase of time pieces,the numerical value of velocity and angular velocity for flying gangue increase,the distance between flying gangue and the person or equipment in lower ends of the working face decreases gradually,and the threat level jointly affected by various variables of flying gangue also changes.In order to avoid the occurrence of flying gangue accidents,protective devices can be set up at the sites where the flying gangue has a high threat level.The theoretical method is consistent with the measured damage degree of the equipment in the lower area of the working face,which further verifies the feasibility of the theoretical method.The application of the evaluation method of flying gangue threat level can provide a certain theoretical basis for the prediction and protection of flying gangue disaster.