The　grain　size　effect　on　deformation　twinning　behavior　of　pure　titanium　during　uniaxial　compression　was　investigated　using　electron　backscattered　diffraction　(EBSD)　technology.　In　this　work,　EBSD　statistical　analyses　on　big　data　sets　of　twins　in　pure　titanium　specimens　with　different　initial　grain　sizes　were　carried　out.　Results　show　that　a　greater　deformation　coordination　ability　caused　by　small　initial　grains　results　in　higher　yield　strength.　Moreover,　upon　increasing　the　grain　size,　more　twin　variants　were　activated　and　more　twin　lamellae　developed.　The　types　of　activated　twins　in　specimens　with　larger　grain　size　were　more　diverse.　The　twin　growth　of　different　twin　modes　was　affected　by　grain　size　differently.　The　volume　of　the　{10-12}　extension　twinning　was　sensitive　to　the　grain　size　due　to　the　small　shear　force　generated　by　it　per　unit　volume.　In　addition　to　grain　size,　grain　orientation　and　the　amount　of　deformation　also　significantly　affect　twinning　activity　during　deformation.　The　primary　twin　lamellae　were　more　abundant　in　the　normal　direction　(ND)　specimens　as　the　deformation　increased,　while　more　lamellar　thickening　occurred　in　the　rolling　direction　(RD)　specimens.　Because　of　more　diverse　primary　twin　modes　in　larger　grains,　the　secondary　twinning　was　also　various.　The　secondary　twinning　{10-12}-＞{11-22}　later　developed.　It　is　speculated　that　the　activation　of　the　secondary　twins　may　be　related　to　the　volume　ratio　of　the　primary　twin　to　the　matrix　grain.　Simultaneously,　the　twin-twin　interactions　were　more　common　in　larger　grains,　restricting　twin　growth　and　promoting　the　material＇s　hardening.　The　types　and　structures　of　twin-twin　interactions　in　specimens　with　large　grain　size　were　also　varied.