The metal Pd is deposited on semiconducting single-walled carbon nanotubes (SWNTs) by physical vapor deposition. The image of scanning electron microscopy shows that the Pd nanoparticles (10—30 nm) are formed on the carbon nanotubes. It is found by the conductive atomic force microscopy that with the increase of Pd nanoparticles, the semiconducting carbon nanotube is changed gradually into a metallic one. Furthermore, our density functional theory calculation demonstrates that with the Pd adsorption increasing the band gap of the SWNT becomes smaller, and eventually disappears, which is in good agreement with the experimental result.