In　the　two-step　open　stope　subsequent　filling　mining　method,　the　determination　of　the　strength　model　for　the　backfill-rock　interface　is　of　great　engineering　significance　to　study　the　stress　distribution　and　stability　of　the　backfill　in　the　stope.　Considering　the　deformation　mechanism　of　the　interface　and　the　interaction　of　the　asperities,　a　strength　model　for　backfill-rock　with　irregular　interface　has　been　proposed　based　on　fractal　theory,　which　can　effectively　describe　the　shear　mechanical　behavior　of　interfaces　with　random　roughness.　The　model　has　been　compared　with　the　two-body　mechanistic　model　and　good　agreements　have　been　achieved.　The　results　show　that　the　shear　strength　of　the　interface　changes　non-linearly　with　increasing　fractal　dimension　D,　when　the　fractal　dimension　D　is　in　the　range　of　1　similar　to　1.12.　The　complete　relationship　between　the　interface　shear　strength　and　the　fractal　dimension　is　given,　as　the　fractal　dimension　increases　from　1　to　2　based　on　the　presented　model.　At　the　same　time,　the　quantitative　relationship　between　the　interface　and　backfill　friction　angles　during　direct　shear　testing　is　analyzed.