A　bistable　composite　tape-spring　(CTS)　structure　is　stable　in　both　extended　and　coiled　configurations,　which　can　be　fully　coiled　or　folded.　Its　bistable　coiling　feature　has　been　employed　in　a　Roll-Out　Solar　Array　and　successfully　deployed　in　space;　its　foldable　characteristics　is　analogous　to　a　flexible　mechanical　hinge,　showing　great　potential　to　be　applied　in　an　aircraft　landing　gear.　Both　the　structural　coiling　and　folding　mechanics　are　dependent　on　tape　geometry;　whilst　the　correlated　scale　effect　has　not　been　investigated,　which　significantly　constrains　its　foldable　mechanical　hinge　designs　and　smart　driving　analysis　in　order　to　further　reduce　weight　and　complexity　for　conventional　mechanical　hinges.　Here,　we　studied　the　folding　stability　mechanics　of　the　CTS　structure　towards　its　full　tape-length　range,　where　novel　stress　and　shape　transitional　mechanisms　are　revealed.　This　is　achieved　by　investigating　the　quasi-static　folding　process　of　the　CTS,　where　new　stable　shape　features　in　terms　of　critical　transitional　length　and　stable　folded　angle　are　observed　and　identified　through　experimental　observations,　finite　element　model,　as　well　as　theoretical　analysis.　Theoretical　criteria　were　then　determined　from　the　strain　energy　analysis　in　comparison　to　the　predefined　folded　tape　shape　features.　The　folding　stability　mechanisms　towards　its　full　tape-length　range　were　proposed　in　order　to　facilitate　customized　flexible　hinge　design　and　in-situ　smart　driving　analysis　in　order　to　replace　conventional　mechanical　hinges.