Abstract: The boundary of caving method should be concerned when the mining method in Xiadian good mine transits from filling to caving method,because in the period of transition the filling stope and caving stope should worked at the same time and the falling of mined-out section roof will affect the filling stope.Based on the investigation in site,the first sublevel caving boundary in Xiadian gold mine is studied in this paper.To simulate this situation,a numerical analysis method,FLAC^3D is applied.The FLAC^3D results show the mined-out section roof have falling after the first sublevel caved,but the plastic zone are formed as vaulted and the displacements attenuation quickly in the boundary of break zone.Scene observation show the falling range not beyond the pillar,and the form of mined-out section falling obeyed the vaulted theory.So designed the boundary of sublevel caving method by the vaulted theory is doable.These results suggest that FLAC^3D can be applied to model the mining behavior of complicated discontinuous rock masses.