The　influence　of　additive　MgO　and　its　content　on　both　the　compressive　strength　and　carbonation　depth　of　alkali-activated　slag　concrete　(AASC)　was　investigated　under　an　accelerated　carbonation　environment.　Furthermore,　the　modification　mechanism　of　MgO　on　the　carbonation　resistance　of　AASC　was　explored　by　multiple　analytical　techniques.　Results　showed　that　the　incorporation　of　MgO　effectively　enhanced　the　post-carbonation　compressive　strength　and　diminished　the　carbonation　depth　of　concrete.　As　the　MgO　content　increased,　there　was　a　gradual　reduction　in　carbonation　depth.　The　incorporation　of　MgO　promotes　the　hydration　of　slag,　altering　the　Al　environment,　and　promoting　the　formation　of　C-S-H　and　Mg-Al　hydrotalcite　phases.　Moreover,　the　addition　of　MgO　resulted　in　the　emergence　of　magnesium　carbonate　and　calcium　magnesium　carbonate　in　the　carbonation　products,　which　filled　the　pores　and　prevented　the　further　diffusion　of　CO2　into　the　interior.　In　addition,　the　improvement　effects　are　more　pronounced　in　the　water　glass　system　compared　to　the　NaOH　system.