Abstract: In view of the relatively thin ore body at the north and south ends of Caolou Iron Mine，in order to avoid the arrangement of mining engineering in the 1st step filling body，reduce the middle mining preparation engineering，and ensure the safety of the high and middle section of the filling method，the structural parameters and stope stability are studied.Based on the investigation of the basic characteristics of mine rock mass and parametric processing，the 2nd step pillar mining scheme of north 4P and south 4P is designed.The rationality of stope span is analyzed by Mathews stability diagram method.The distribution of displacement，stress and plastic zone after mining in the middle section of -410 m and -350 m is simu⁃ lated by FLAC3D software，and the implementation effect is quantitatively evaluated by 3D laser scanning. The analysis of the relationship between the stability number of the roof and floor，ore body and filling body and the hydraulic radius of the stope by Mathews stability diagram method shows that the north 4P stope is 46 m long，23 m span，110 m high and 3.5 m wall protection pillar is set，and the south 4P stope is 30 m long，27 m span，110 m high and 2.5 ~3.5 m wall protection pillar is set.The structural parame⁃ ters of the two test stopes are reasonable and the stope can be kept stable.The maximum displacement of numerical simulation is small and concentrated in 1/3 of the hanging wall in the middle of the room and the top pillar，which are 4.48 cm and 5.56 cm respectively.The minimum tensile stress of the surrounding rock is 2.45 MPa and 3.1 MPa respectively，and the maximum compressive stress is 31 MPa and 27.5 MPa respectively，which do not exceed the strength of the surrounding rock.The distribution of plastic zone in stope is controllable.In the industrial test，there was no collapse of the filling body，the size of the empty area met the design requirements，the recovery rate was 90%，and the waste rock mixing rate was 7%.The study verified the technical feasibility of the 110 m parallel mining of the 2nd step pillar，and provided a theoretical basis and engineering reference for the efficient and safe mining of the 2nd step stope under sim⁃ ilar surrounding rock conditions.

Key words: 2nd step stope, stope stability, Mathews graphic method, numerical simulation