The　addition　of　alloying　elements　during　additive　manufacturing　increases　the　strength　but　always　sacrifices　ductility.　Therefore,　simultaneously　enhancing　strength　and　ductility　is　still　the　focus　today.　In　this　study,　Cu　was　selected　as　the　alloying　element,　and　the　optimal　Cu　addition　(1.2　wt%)　was　re-alloyed　and　predicted　using　Thermo-Calc　software　combined　with　a　single-bead　deposition　experiment,　followed　by　alloying　into　feeding　wire.　Ti-6Al-4V-1.2Cu　was　compared　with　commercial　Ti-6Al-4V　deposits,　and　it　was　found　that　both　microstructures　consisted　of　prior　beta,　GB　alpha,　and　basketweave　structures　containing　alpha+beta　lamellae.　The　introduction　of　Cu　realized　the　refinement　of　prior　beta　grains　(836　+/-　12　mu　m　-＞　592　+/-　8　mu　m),　the　refinement　of　alpha　laths　(2.56　+/-　0.06　mu　m　-＞　1.91　+/-　0.04　mu　m),　the　coarsening　of　beta　laths　(0.03　+/-　0.005　mu　m　-＞　0.2　+/-　0.03　mu　m),　and　the　refinement　of　GB　alpha　(0.9　+/-　0.07　mu　m　-＞　0.45　+/-　0.04　mu　m).　As　a　beta　stabilizer,　Cu　increased　the　residual　beta　content　in　the　final　microstructure　(8.89%-＞　18.67%).　No　formation　of　brittle　Ti2Cu　means　that　only　grain　refinement　strengthening　and　solid-solution　strengthening　matter.　The　yield　strength　increased　from　868.23　MPa　to　934.32　MPa　(7.61%　increase).　Among　them,　the　contribution　ratio　of　grain　refinement　strengthening　and　solid　solution　strengthening　was　the　same　through　quantitative　analysis.　The　ultimate　tensile　strength　increased　from　934.97　MPa　to　990.97　MPa　(6%　increase).　At　the　same　time,　tensile　fracture　elongation　increased　from　6.35%　to　10.66%　(67.87%　increase),　while　the　fracture　mode　transits　from　brittle　cleavage　to　ductile　dimples.　Grain　refinement　of　prior　beta　grains,　alpha　laths,　and　GB　alpha,　inhibition　of　the　beta　-＞alpha　＇　martensitic　transformation,　and　local　misorientation　change　of　alpha　laths　are　the　main　factors　in　improved　ductility.　In　addition,　the　UTS　and　EL　results　are　compared　with　earlier　studies　to　reveal　the　prospect　of　this　research.