Spherical　cobalt　nanoparticles　were　reduced　and　deposited　in　situ　on　the　graphene　(GNP)　surface　using　a　novel　hydrothermal　method,　and　the　prepared　Co@GNPs　reinforced　powder　were　uniformly　dispersed　in　the　alloy　matrix.　The　Co@GNPs/CoCrMo　composite　fabricated　using　selective　laser　melting　(SLM)　was　densely　organized　with　reduced　hole　defects,　and　fine　equiaxed　grains,　elongated　columnar　grains,　and　duplex　e　+　gamma　were　observed　in　the　composite　organization.　Meanwhile,　a　high　density　of　dislocations　and　nanoscale　stacked　layer　dislocations　were　observed　at　the　equiaxed　grain　boundaries.　Further,　the　GNPs　acted　as　heterogeneous　nucleation　sites,　which　promoted　the　transformation　of　the　gamma-Co　(FCC)　austenite　phase　to　the　e-Co　(HCP)　martensite　phase　by　means　of　slip.　A　unique　characteristic　structure　of　nanoscale　parallel-arranged　lath　martensite　is　formed　on　the　surface　of　GNPs.　Therefore,　a　co-lattice　structure　between　e-co　and　gamma-co　shows　the　specific　orientation　relationship　between　the　crystallographic　plane　(1　1　1)gamma-co//(0　0　0　2)e-co　and　the　crystallographic　zone　axis　[1　1　0]gamma　co//[1　1　2　0]e-co.