Nanoscaled　deformation　twins　have　been　observed　in　cold　sprayed　Cu　coatings　and　the　coating　hardness　has　been　improved　by　this　kind　of　tiny　twins.　Strain　rate　up　to　10(9)　s(-1)　at　the　impact　interfaces　can　be　achieved　at　the　cold　spray　process,　and　the　maximum　shearing　compressive　stress　and　tensile　stress　are　392　MPa　and　397　MPa,　respectively,　obtained　from　impacting　simulations.　They　are　larger　than　the　required　shearing　stress　for　the　formation　of　deformation　twins　in　Cu.　The　orientation　relationship　between　the　stripes　can　be　determined　to　be　(11　(1)　over　bar)(M)　parallel　to　(11　(1)　over　bar)(T)　and　((1)　over　bar　10)(M)　parallel　to　(101)(T)　both　in　coatings　prepared　by　cold　spray　Cu　particles　annealed　at　700　degrees　C　and　250　degrees　C,　respectively.　The　hardness　of　the　coatings　is　higher　than　that　of　the　corresponding　substrates　which　indicates　the　improvement　by　the　work　hardening　effect　in　the　cold　spray　process.　Though　the　misorientation　of　the　deformation　twins　in　the　coatings　slightly　deviates　from　60　degrees,　the　existence　of　nanoscaled　deformation　twins　improves　its　hardness　significantly.