The　Mg2Si　reinforced　Mg-2Al-Zn-2Gd　composite　was　synthesized　by　in-situ　solid　state　reaction　and　repeated　plastic　deformation　(RPW)　process.　The　XRD,　SEM　and　TEM　analysis　results　indicate　that　the　RPW　method　can　significantly　decrease　the　second　phase　particle　size　as　well　as　the　matrix　crystalline　size,　and　the　elastic　modulus　and　yield　strength　of　the　composite　increase　with　increasing　the　volume　fraction　of　Mg2Si　whereas　the　fracture　strength　and　strain　decrease.　The　interface　between　Mg2Si　and　matrix　is　smooth,　and　no　crack　initiation　source　has　been　found　on　the　interface.　The　propagation　of　cracks　formed　in　matrix　during　fracture　can　be　obstructed　by　the　second　phase,　and　the　increase　of　mechanical　properties　of　the　composite　is　attributed　to　the　dispersed　Mg2Si　second　phase　particle　and　the　refined　matrix　grain　size.