The ore body of Yongshaba mine in Guizhou Kaiyang Phosphorite Group Company is a gently inclined one.It uses the mechanized sub-fill mining method panel mining.The study of the relationship between stope span and roof stability ensures the safety of operating personnel and stable production.According to the rock mechanical properties,this paper establishes the models with the different stope span under the program without supporting.The numerical simulations show that the stope overall displacement nearly obeys symmetrical distribution;surrounding rock near the excavation boundary has the maximum displacement,and the movement direction points towards gob;Stope roof without supporting can maintain its own stability in the span of 20 m,while the span increases to 25 m,the roof begins to be damaged.