Ore recovery depends on the stope structure parameters, at the same time, stope safety will be changed according to difference stope structure parameters. A mechanics model of stope structure of room and pillar mining method is established with FLAC3D, a finite difference software, in this paper. And the stope stability changing with crustal stress and stope structure parameters is simulated. The results of numerical simulation indicate that when mining level orebody with room and pillar mining method, tensile stress in central roof linearly decreases along with the increase of lateral pressure coefficient, and the influence of lateral pressure to tensile stress in roof near the pillar is obvious. The roof's maximum tensile stress and pillar's average vertical stress are increased with the increase of vertical stress, which makes the safety of stope decreased. And the roof's maximum tensile stress is hardly changed with the pillar height; but increased with the increase of room span. So it can be seen that the roof's stability can be improved by increasing the pillar size.