The　{10-12}　twinning　activities　of　Mg-3Al-1Zn　magnesium　alloy　during　multi-directional　compression　were　investigated　by　in　situ　EBSD　technology.　The　specimen　was　pre-compressed　to　a　strain　of　3.2%　along　TD,　followed　by　a　compression　with　a　strain　of　2.6%　along　RD,　and　finally　a　compression　with　a　strain　of　2.5%　along　TD.　The　Schmid　factor,　strain　compatibility　factor　(m)　and　twinning　strain　tensor　(epsilon)　were　calculated　to　analyze　the　twinning　variant　selection.　The　results　show　that　four　types　of　twinning　behaviors　can　be　observed　during　multi-directional　compression:　(1)　the　growth　of　twin　lamellas　generated　from　previous　compression;　(2)　the　nucleation　of　new　{10-12}　twins　in　existing　twins;　(3)　the　nucleation　of　new　{10-12}　twins　in　initial　grains;　and　(4)　detwinning.　Some　grains　show　only　one　twinning　behavior　within　a　grain,　while　some　grains　exhibit　two　or　more　twinning　behaviors　within　a　single　grain.　The　variant　selection　of　{10-12}　twins　for　twin　pairs　and　twin　chains　in　neighboring　grains　is　dominated　by　high　Schmid　factor　and　high　strain　compatibility　factor.　Because　of　good　accommodation　between　neighboring　grains,　the　simultaneous　detwinning　and　retwinning　behaviors　developed　in　twin　pairs　or　twin　chains　during　multi-directional　compression.