The　ability　of　loosely　focused　picosecond　laser　to　induce　filamentation　(4.8　times　the　Rayleigh　length)　in　sapphire　was　confirmed.　The　morphology　and　microstructure　of　the　filamentary　traces　under　typical　pulse　energy　were　studied,　in　which　the　colorful　birefringence　phenomenon　and　damage　defects　were　detected　in　sapphire.　Irreversible　ceramic-like　polycrystalline　microstructures　were　formed　in　filamentary　traces,　and　the　phase　transition　from　alpha-Al2O3　to　gamma-Al2O3　directly　reflected　the　thermal　effect　of　picosecond　laser　filamentation.　According　to　the　filamentary　characteristics,　a　continuous　filamentary　channel　with　a　uniform　diameter　of　33　mu　m　and　a　length　of　7443　mu　m　was　obtained　by　gradually　raising　the　focal　position.　The　research　provides　first-hand　information　for　the　high　throughput　micro-cutting,　micro　drilling　and　thin　slicing　of　sapphire　based　on　ultrafast　laser　non-linear　effects.