The　evolutionary　features　of　the　microstructure　and　the　second　phase　particles　during　high　velocity　impact　deformation　were　investigated　by　using　scanning　electron　microscope　and　transmission　electron　microscope.　The　experimental　results　show　that　the　nano-scale　precipitates　(Al2Cu)　with　needle　shape　have　been　partly　dissolved　due　to　local　temperature　risen　by　bullet　impact.　Since　the　micron-scale　second　phase　(Al2Cu)　with　spherical　or　near-spherical　shape　was　difficult　to　deform　during　bullet　impact,　it　resulted　in　sectional　stress　concentration,　leading　to　the　formation　and　early　enlargement　of　micro-cracks.