Abstract: Used the open-pit blasting of Nanfen Iron Open-pit Mine and its main haulage tunnel as work background,according to the great number of tested data of blast vibration,a new sudden applied load method based on displacement equivalent principle was set forth to simulate the process of blast seismic wave propagation in rock medium by Dynamic FEM.The stability of the tunnel was analyzed in this method.The damping factor,the ultimate quantity of explosive per blast and the ultimate endurable speed of the tunnel system were obtained.The results indicate that the method is easy and effective.