Carbon　nanotubes　were　prepared　using　electric-arc　method.　The　effect　of　catalysts　of　iron,　cobalt,　nickel　and　mixed　catalysts　on　the　formation　of　carbon　nanotubes　was　investigated.　The　influence　of　shape,　location　and　dimension　of　the　graphite　electrode　on　electric-arc　stability　was　studied.　Carbon　nanotubes　were　formed　with　different　cooling　gas　media.　Samples　purified　using　nitric　acid　oxidation　and　atmospheric　oxidation　were　observed　by　transmission　electron　microscopy　(TEM).　Higher　yield　of　carbon　nanotubes　is　achieved　under　conditions　of　low　current　and　voltage,　using　dual-metal　catalysts　and　mixed　cooling　media.　The　results　show　an　increase　of　50%-115%　and　75%　in　yield　comparing　to　that　using　the　single　metal　catalyst　and　single　cooling　medium.　The　carbon　nanotube　samples　observed　by　TEM　were　relatively　straight,　with　longest　length　of　over　8　μm　and　diameter　of　about　10　nm,　and　consisted　of　both　single-wall　nanotubes　and　multi-wall　nanotubes.