A　bistable　composite　cylindrical　structure　is　a　thin-walled　shell,　stable　in　its　extended　and　coiled　configurations,　that　offers　large　shape-morphing　capabilities　without　structural　damage.　It　has　been　successfully　applied　to　deployable　structures　and　launched　into　orbit.　Smart-morphing　designs　provide　new　freedom　and　flexibility　for　space-deployable　mechanics,　reducing　structural　weight　and　complexity.　Here,　we　present　a　novel　magnetically　activated　bistable　composite　cylindrical　structure,　where　the　fundamentals　of　the　critical　magnetic　driving　boundaries　are　revealed　for　the　first　time　to　develop　a　reversed　smart-morphing　design　principle.　This　is　achieved　by　employing　a　magnetically　responsive　area　within　a　bistable　composite,　where　the　NdFeB　particles　are　co-cured　directly　with　the　carbon　layups　to　ensure　good　bonding.　Theoretical　analysis　of　the　magnetic　driving　principle　was　developed　to　reveal　the　interacting　mechanics　of　a　bistable　structure　subjected　to　magnetic　actuation.　The　magnetic　field　distribution　was　characterized　through　experiments;　a　series　of　magnetic-responsive　bistable　composite　cylindrical　samples　were　produced　and　subjected　to　magnetic　activation　to　determine　the　critical　shape　transition　intensities.　Their　shape-changing　processes　were　also　evaluated　through　mechanical　testing　and　compared　to　the　magnetic　driving　mechanics.　It　is　found　that　there　is　an　optimal　level　of　magnetic　particle　concentration　to　minimize　the　magnetically　responsive　time　and　input　energy.　The　critical　boundaries　in　terms　of　the　current　and　air　gap　are　established　through　theoretical　analysis　and　verified　through　experimental　observations.　The　magnetic　driving　mechanics　are　then　discussed　and　concluded　in　detail.　This　provides　a　simple　and　effective　alternative　for　smart　actuation　and　morphing　control　of　bistable　composite　structures,　supporting　their　future　applications　in　deep　space　exploration.