There　is　a　serious　challenge　to　the　safe　operation　of　orbiting　satellites　as　the　number　of　space　debris　on　the　geosynchronous　orbit　increases.　Consequently,　the　active　removal　of　space　debris　has　drawn　wide　attention　in　recent　years.　And　a　tethered　system　is　considered　to　be　a　promising　method　to　remove　debris　in　high　orbit　with　its　low　power　consumption　and　costs.　However,　the　flexible　tether　of　the　system　can　bring　the　coupling　of　the　orbit　motion,　the　sway　motion　and　the　variation　of　large　debris　attitude,　which　means　great　danger　in　deorbiting　phase　and　bring　a　huge　challenge　in　later　control.　Hence,　in　this　paper,　aiming　to　de-orbit　large　space　debris　safely　with　a　tethered　system,　a　multi-stage　horizontal　drag　de-orbit　strategy　is　designed　to　deal　with　the　coupling　caused　by　a　flexible　tether.　Based　on　that,　optimal　commands　are　planed　using　Gaussian　pseudo　spectral　method　to　achieve　decoupling　of　the　orbit　motion,　the　sway　motion　and　the　variation　of　target　attitude.　Finally,　numerical　simulation　is　established　to　follow　the　planned　commands　by　tension　and　tug　thrusts　in　large　space　debris　removal　to　verify　the　effectiveness　of　the　proposed　de-orbit　strategy.