Safety is an extremely important part of mine production. The cantilever structure of filling body is common form of potential safety hazard in drift stoping of Longshou mine. Collapse is easy to occur due to self weight and deep in-situ stress. Longshou mine is the only large underground mine in China that successfully adopts panel area mechanized downward hexagonal drift cemented filling mining method，its artificial false roof cantilever and filling cantilever surrounding rock often collapse by itself. At the same time，the deep filling body has large deformation，which brings great instability and hidden dangers to the safety production of the mining area. In order to effectively deal with and comprehensively evaluate the cantilever stability of backfill，based on the cantilever beam theory and combined with the experience of geotechnical dangerous rock mass，this paper established the mechanical models of artificial false roof cantilever and surrounding rock filling cantilever in Longshou mine，and studied the calculation methods of collapse and tension crack fall deformation and failure modes. Thus，the limit cantilever length and stability coefficient K of filling body were proposed. The limit length of cantilever was calculated theoretically，verified by numerical simulation and stability coefficient K. The results show that the stability of the filling cantilever is negatively correlated not only with the limit length of the cantilever，but also with the development of the overlying crack. Through the simulation，the tensile strength of the failure condition is basically the same between the theoretical limit length and the simulated length. It shows that the theoretical limit length is suitable for the actual geological conditions of Longshou mine. At the same time，the stability coefficient K can effectively count the cantilever state of the filling body under different crack conditions，and judge the crack depth ratio at the top of the cantilever of the filling body according to the actual state of the cantilever on site and in combination with the stability evaluation grade classification table. Therefore，the cantilever limit length and stability coefficient K can effectively evaluate the stability of the filling cantilever in Longshou mine. The practical application is simple，and the calculation results are basically consistent with the field investigation results. It can play a timely early warning effect for the danger caused by the excessive cantilever and the further development of cracks. It has guiding significance for the safety production of drift mining in Longshou mine.