Surface　etched　graphene　nanoplatelets　(SEGs)　were　obtained　by　KOH　etching　of　reduced　graphene　oxides,　and　the　etching　degree　was　controlled　by　KOH　addition.　Nano-sized　pores　with　diameters　mainly　around　1　nm　and　4　nm　were　created　on　the　surface　carbon　layer　of　SEGs.　During　the　composite　preparation,　the　nanopores　on　SEGs　provided　nucleation　sites　and　suppressed　the　growth　of　Mg　crystal,　which　led　to　Mg　nanograins.　The　mechanical　deformation　(hot　extrusion)　and　nanocrystalline　structures　promoted　Mg　amorphization　transition　on　the　interface.　The　absorbed　and　residual　oxygen　on　SEGs　reacted　with　Mg　into　MgO　nanoparticles.　These　nanoparticles　(Mg　nanograins,　MgO　nanograins　and　amorphous　Mg)　respectively　had　coherent,　semi-coherent　and　incoherent　interface　with　Mg　matrix,　which　caused　dislocations　and　lattice　mismatch　regions　along　the　interface.　The　resulting　heterogeneous　interface　of　SEGs/nanoparticles/Mg　matrix　built　a　nano-micro　hierarchical　structure,　which　largely　enhanced　the　strength　and　ductility　of　SEGs/ZK61　composites.　The　SEG-4/ZK61　composite　exhibited　optimum　mechanical　performance　with　yield　strength　of　236　MPa,　ultimate　tensile　strength　of　337　MPa,　and　especially　elongation　of　32　%.　This　work　develops　nanopore-modified　graphene　to　reinforce　Mg　alloys,　which　might　provide　a　design　guideline　for　high　performance　metal　matrix　composites.