Mg　alloy　has　hexagonal　structure　and　exhibits　poor　workability　at　room　temperature,　which　is　attributed　to　the　difficulty　in　activating　a　sufficient　number　of　independent　slips　to　accommodate　the　deformation.　Twinning　plays　an　important　role　in　plastic　deformation　of　Mg　alloys　during　low　and　medium　temperature　to　accommodate　the　imposed　strain,　especially　the　strain　along　the　c-axis.　Therefore,　the　microstructure　and　texture　evolutions　of　AZ31　Mg　alloy　during　multi-pass　compressions　at　room　temperature　were　investigated　by　EBSD　technology.　The　results　show　that　the　microstructure　and　texture　evolutions　are　mainly　controlled　by　tension　twinning　during　multi-pass　compression.　And　the　more　the　strain　passes,　the　severer　the　texture　transformation.　The　c-axes　of　the　grains　are　almost　rotated　to　the　compression　direction　by　tension　twins.　The　twins　generated　during　multi-directional　compression　can　separate　grains　and　then　refine　them.　However,　the　de-twinning　can　rotate　the　grains　back　to　the　initial　orientations,　which　is　against　the　texture　weakening.　The　Schmid　law　governs　the　characteristics　of　{10　(1)　over　bar2}　twinning,　and　thus　controls　the　texture　evolution.　Both　the　residual　matrix　and　the　pre-deformation　induced　twins　intersect　with　the　twins　generated　during　subsequent　deformation.　And　this　can　separate　the　grains　and　weaken　the　texture　strength.　The　number　and　morphology　of　the　activated　twin　behavior　during　multi-pass　compression　would　be　influenced　by　the　pass　reductions,　consequently　affecting　the　grain　refinement.