Carbon nanotubes are one-dimensional materials by rolling up graphitic layers to form a seamless tubular structure.Its Sp2 hybridized and six-six carbon ring atomic structure exhibits extraordinary electrical property.Depending on its chiral angle, it can be semiconducting with high electron mobility.Recently, scientists in Stanford Univ of USA reported the exceptional high on-off ratio of 105-6, as using near pure (10,5) tube.In the present work, we reported the controlled synthesis of 100 mm long, semiconducting triple-walled carbon nanotubes by a gas flow assisted chemical vapor deposition method [1,2], where we use methane as carbon source,iron as the catalyst and Si as the substrate.Electronic diffraction characterization suggested there have 35 mm long sections with the uniform (n,m) value.