Carbon nanotubes, as a successful conducting agent for power lithium ion cathode, have been applied in a large scale. Among the production of carbon nanotubes, the purification of carbon nanotubes is an important step for the application in lithium ion power battery. In this paper, physical purification, instead of chemical purification, of as-carbon nanotube soot in an Acheson furnace was investigated. The carbon nanotubes were first purified in an Acheson furnace at 3 000 ℃ and 2 800 ℃ respectively. Then, metal content, burning residue content of these purified carbon nanotubes were measured with ICP, EDS, and thermos-gravimetric analysis (TGA). And their resistivity were detected with a four-probe film resistance instrument. The micro structure and surface characteristics of these carbon nanotubes purified at different temperatures were characterized by SEM, XRD, FT-IR. The results show that the carbon nanotubes purified respectively at different high temperatures in Acheson furnace can be effectively reduced in metal content and burning residues, and these carbon nanotubes, as conductive agent can meet the requirements of power battery. Compared with the non-purified carbon nanotubes, the resistivity of carbon nanotubes purified at 3 000 ℃ decreases significantly and the crystallization degree of graphite increases, while the resistivity of carbon nanotubes purified at 2 800 ℃ increases slightly, the degree of graphite crystallization did not change much, and the quantity of their surface functional groups decreases.