Twinning　structures　and　their　interfacial　segregation　play　a　key　role　in　strengthening　of　magnesium　alloys.　Micro-steps　are　frequently　existed　in　the　incoherent　twin　boundaries,　while　the　effect　of　them　on　interface　and　interfacial　segregation　is　still　not　clear.　In　this　work,　we　performed　an　atomic-scale　microstructure　analysis　using　high-angle　annular　dark　field　scanning　transmission　electron　microscopy　(HAADF-STEM)　to　explore　the　effect　of　micro-steps　on　twin　and　its　interfacial　segregation　in　Mg-Ag　alloy.　Diffraction　pattern　of　the　incoherent　twin　shows　that　the　misorientation　has　a　slight　tilt　of　5　degrees　from　its　theoretical　angle　of　125　degrees　due　to　the　accumulated　effects　of　the　micro-steps　and　their　misfit　dislocations　in　twin　boundaries.　Most　of　the　micro-steps　in　twin　boundary　are　in　the　height　of　respectively,　and　both　of　them　have　two　types　according　to　whether　there　are　dislocations　on　the　micro-steps.　The　twin　boundary　is　interrupted　by　many　micro-steps,　which　leads　to　a　step-line　distributed　interfacial　segregation.　Moreover,　the　Ag　tends　to　segregate　to　dislocation　cores,　which　results　in　the　interruption　of　interfacial　segregation　at　the　micro-steps　with　dislocations.