The　mixed　Sn　and　Cu　powder　was　milled　by　mechanical　ball　milling.　The　milled　powders　were　analyzed　by　X-ray　diffraction,　differential　thermal　analyzer　and　scanning　electron　microscopy.　The　effect　of　ball　milling　conditions　on　the　formation　of　Sn-0.7Cu　alloy　was　investigated.　The　results　showed　that　voltage,　ball-to-powder　mass　ratio　and　milling　time　affect　the　formation　of　Sn-0.7Cu　alloy　significantly.　The　mechanism　of　mechanical　alloying　Sn-Cu　was　that　the　mechanically-induced　atom　diffusion　drives　substitutional　solid　solution　and　interface　dissolution,　as　a　result　of　which　Cu6Sn5　was　formed.