Abstract: According to the conditions of parallel belt at low-grade iron ore deposits in southeast area of Gongchangling Iron Mine and control requirements of surface subsidence area caused by high drop mining，the problems of the low productivity and poor benefit created by using conventional cut filling method are analyzed to control surface rock movement，the control action of granular in collapse pit to the solid side wall is studied，and a new filling approach for controlling the range of the surface subsidence by using the critical medium column theory is proposed.In the paper，the arch conditions of moving granular is studied on trial，which reveals the continuity of granular flow in collapse pit，and draws the conclusion that filling waste rock into collapse sink would not cause arch and fall hazard.The composition of collapse pit wall is observed and analyzed to reveal the characteristics that the surrounding rocks slide or chip mainly along the weak structural plane，and accordingly safety filling measures that the filling waste cooperative emissions along the collapse pit axial and radial is put forward to prevent side wall slipping；In addition，the large structural parameters sublevel caving is adopted for underground to increase mining intensity and balance the decline rate of granular in collapse pit，which forms the open-pit and underground cooperative mining and filling methods.It is proved by theoretical analysis and industrial experiments that the method above can enhance production efficiency and improve the working environment largely，and create an environmental protection and high efficient mining approach for the steep iron deposits with low-grade parallel belt.

Key words: Cooperative mining, Surface subsidence, Critical medium column, Mining and filling technology