Abstract: In view of the characteristics of the large goaf of jianlin hill, Daye iron mine (with horizontal exposed area of the roof being 6434m2 , and the height being 45m) , are conducted the geological investigation, vibration measurement, geomechanical tests, 3-dimensional BEM analysis, photoelastical tests and dynamics model tests. The comprehensive studies gave the conclusion that the goaf is basically stable and can undergo mining under the condition of monitoring and restriction of blasting jobs. At the present the mining in No.1 ore body has been finished and the large goaf still remains basically stable with it length of 200m, width of 78m and height of 73m, and the maximum horizontal exposed area of 9850m2. The conclusion proved to be correct and had led to an apparent economical affects. It is a typical example of the application of rock dynamics in the engineering and have significance for appraisal of the stability of the large goaf in similar mines.