For mines transformed from caving method to filling method, under the influence of caving method, the mine's geological conditions will become relatively complex, the integrity and stability of surrounding rock are relatively poor and the mining technical conditions are relatively complex either.In order to ensure the safety of the next production operation of the mine, it's necessary to set a security pillar between the caving method stope and the filling method stope.In this paper, combined with the actual engineering geological conditions of the mine, a variety of theoretical analysis methods represented by the elastic small sheet theory considering the dynamic load of the goaf roof collapse are used to determine the size of the horizontal isolation pillar between the caving method and the filling method.Combined with the movement parameters of mine surrounding rock and Bieniawski pillar strength theory, the size of isolation pillar between stopes of caving method and filling method is calculated.Meanwhile, the rationality of the size of security pillar is verified by Phase2 two-dimensional numerical simulation, and the smooth transition from caving method to filling method was finally realized.On the basis of ensuring the safety of mining in the next step, the recovery rate of ore is improved and certain economic benefits are created for the mine.