As-annealed　commercial　pure　titanium　(grade　1)　was　selected　as　a　model　material　whose　crystalline　structure　was　hexagonal　close-packed.　The　evolution　of　the　microstructure　and　micro-orientation　induced　by　high-speed　compression　was　characterized　to　elaborate　the　formation　mechanism　of　the　high-speed　deformation　characteristic　microstructure　in　a-titanium.　Twinning　played　a　coordinating　role　for　dislocation　slipping　that　was　the　main　plastic　deformation　mechanism.　The　high-speed　deformation　characteristic　microstructure　of　as-annealed　commercial　pure　titanium　was　an　adiabatic　shear　band　(ASB)　with　an　average　width　of　50　mu　m　at　a　strain　rate　of　5400　s(-1),　whose　initial　grains　were　0.5-1.0　mu　m　in　size.　The　formation　and　extension　of　ASB　were　attributed　to　the　interaction　between　the　shear　stress　and　the　adiabatic　temperature　rise.　A　formation　model　of　ASB　in　alpha-Ti　was　proposed　in　terms　of　the　formation　mechanism　of　the　high-speed　deformation　characteristic　microstructure.