There　is　a　serious　challenge　to　the　safe　operation　of　orbiting　satellites　as　the　number　of　space　debris　increases　for　its　high　risks　and　the　possible　crippling　effects　of　collisions.　Consequently,　the　active　removal　scenario　of　space　debris　has　drawn　wide　attention　in　recent　years,　and　a　tethered　system　is　considered　to　be　a　promising　method　for　its　large　operating　distance　and　low　power　consumption.　However,　the　flexible　tether　of　the　system　will　bring　the　coupling　of　the　orbit　motion,　the　sway　motion　and　the　variation　of　large　debris　attitude,　which　brings　about　great　danger　in　de-orbiting　phase　and　a　huge　challenge　in　later　control.　Hence,　aiming　to　de-orbit　large　space　debris　safely　with　a　tethered　system,　a　multi-stage　horizontal　drag　de-orbit　strategy　that　consists　of　two　stages　is　designed.　At　the　first　stage,　the　orbit　altitude　is　rose　with　a　tug　thrust　whose　direction　is　consistent　with　the　tether,　which　does　not　provoke　the　in-plane　oscillation　of　the　tethered　system.　At　the　second　stage,　the　orbit　is　circularized　by　changing　the　size　and　direction　of　the　tug　thrust.　Especially,　optimal　commands　based　on　the　minimum　of　tangling　risks　are　planned　using　Gauss　pseudospectral　method　to　avoid　target　tangling　and　achieve　decoupling　of　the　orbit　motion,　the　sway　motion　and　the　variation　of　the　target　attitude.　Then,　the　stable　attitude　control　of　the　tethered　system　is　achieved　by　designing　a　hybrid　fuzzy　adaptive　proportion　differentiation　(PD)　with　hierarchical　sliding-mode　controller　(HSMC)　in　the　de-orbit　process.　Finally,　numerical　simulation　is　implemented　to　verify　the　effectiveness　of　the　proposed　de-orbit　design.