Abstract: The multi-layer gently inclined thin-medium thick ore body is recognized as a difficult ore body in the mining industry. The deep ore body outside the open-pit mining boundary of the No. 2 min⁃ ing area of Kunyang Phosphate Mine has more special geological conditions. It is produced by double-layer phosphate rock with waste rock，and the hanging wall rock and interlayer have poor stability. Firstly，the mining technical conditions are analyzed，and the rock mass quality is classified by Proctor classification method and RMR classification method respectively. It is concluded that Kunyang Phosphate rock belongs to poor rock mass-general rock mass. Combined with the mining technical conditions，the underground mining scheme of the ore body is studied，and a variety of mining methods suitable for the underground mining of the deep ore body outside the open-pit mining boundary of the No.2 mining area of Kunyang Phosphate Mine are proposed. Qualitative and quantitative comparisons are carried out，and the advantages and disadvantages of different methods are analyzed from the perspective of safety，technology and econo⁃ my. Finally，the room pillar subsequent filling mining method is recommended，and the non explosive con⁃ tinuous cutting and mining process of tunneling machine is adopted，It provides support for the conversion of open-pit mining to underground mining in the second mine of Kunyang Phosphate Mine.

Key words: gently inclined medium-thick orebodies, room pillar subsequent filling mining method, non explosive continuous cutting and mining process of tunneling machine