{10　(1)　over　bar1　}　compression　twins　with　high　density　stacking　faults　were　studied　at　atomic　scale　using　Cs-correction　transmission　electron　microscopy.　On　one　side　of　the　{10　(1)　over　bar1}　twin　boundary,　there　were　many　steps　arranged　alternately　with　the　coherent　twin　boundaries.　Most　of　the　steps　were　linked　with　stacking　faults　inside　twins.　Burgers　vector　of　twinning　dislocations　and　the　mismatch　strain　at　steps　were　characterized.　Due　to　the　compressive　mismatch　strain　at　steps,　the　high　density　stacking　faults　inside　twins　were　formed　at　twin　tips　during　twinning　process.　The　localized　strain　at　the　steps　would　be　related　to　the　crack　nucleation　in　magnesium　alloys.　(C)　2019　Published　by　Elsevier　Ltd　on　behalf　of　The　editorial　office　of　Journal　of　Materials　Science　&　Technology.