Abstract: In order to solve the problem of recovering coal resources under ground buildings at Linxi coal mine，combined with its geological conditions of large embedded depth and hard roof，smaller mining width and larger retaining width were adopted when strip mining，the secondary strip mining was carried out in the reserved coal pillar，after a period of time when the surface deformation stabilized．Based on the key strata theory，the strip mining and the secondary strip mining were studied by using the methods of the oretical analysis，numerical simulation and field measurement；the inferior key strata 1 was put forward as mining design basis；then the strip mining scheme can be determined，the mining width and retaining width were respectively 60 m and 120 m；the roadway driving along next goaf with narrow coal pillar was adopted when secondary strip mining，the mining width was 60 m and the retaining width was 55 m．The results show that the surface subsidence deformation is controlled by the inferior key strata 1；the destruction of surface deformation caused by strip mining and secondary strip mining to buildings is in damage grade I．The industrial test has been conducted at Nine-East area，then good results have been achieved．

Key words: deep mining, hard roof, key strata theory, strip mining, secondary strip mining