A method for preparing a carbon nanotube catalyst having metal catalyst nanoparticles supported on the inner channel of the carbon nanotube catalyst, comprising the steps of: removing carbon impurities from said carbon nanotube by heat treatment, and then removing catalyst components by hydrochloric treatment (step 1); immersing the hydrochloric acid-treated carbon nanotube in a mixed acid solution and sonicating the resulted solution (step 2); washing several times the surface of the sonicated carbon nanotube from step 2 with distilled water at room temperature under atmospheric pressure and filtered, leaving the resulting product standing at ambient temperature for 30-360 minutes and subjecting the resulted product to vacuum drying (step 3); and supporting metal catalyst nanoparticles on the inner channel of the carbon nanotube by CVD, while feeding a flow of metal precursors to the vacuum-dried carbon nanotube (step 4), wherein the heating process in step 1 for removing carbon impurities from the carbon nanotube catalyst is conducted in an oven heated to 450-550°C under air atmosphere for 30 minutes to 2 hours, and the treatment with hydrochloric acid is carried out by immersing the carbon nanotube in hydrochloric acid (6-10 mol), maintaining it therein for 6-24 hours, then washing with distilled water and drying in an oven at the temperature of 100-120°C for 12 to 24 hours, wherein the carbon nanotube treated with hydrochloric acid in step 2 is immersed in a mixed acid solution in which 14M nitric acid and 98% sulfuric acid are mixed at the mixing ratio of 1:1 by volume, and sonicated for 3-10 minutes, wherein the vacuum drying process in the step 3 is performed in an oven at the temperature of 100-120°C for 30 minutes to 2 hours, and wherein the metal catalyst nanoparticles supported on the carbon nanotube in step 4 include particles of platinum (Pt), ruthenium (Ru), nickel (Ni), cobalt (Co) or molybdenum (Mo), wherein the metal particles are provided in the form of metal precursors so as to be supported on the inner channel of the carbon nanotube, wherein platinum precursors are selected from the group consisting of methyltrimethylcyclopentadienyl-platinum (MeCpPtMe 3), Pt(Me) 3 (Cp), Pt(Tfacac) 2, Pt(Me) (Cp), Pt(Me) 2, [PtMe 3 (acac)] 2 (acac; acetylacetonato ligand), PtCl 2 2, Pt(PF 3) 4, Pt(acac) 2, and Pt(C 2 H 4) 3; ruthenium precursors include ruthenium acetylacetonate (Ru(acac) 3) or ruthenium carbonyl (Ru 5); nickel precursors include nickel nitrate (Ni(NO 3) 2) or nickel carbonyl (Ni 4); cobalt precursors include Co 3 NO; and molybdenum precursors include Mo 6. removing carbon impurities from said carbon nanotube by heat treatment, and then removing catalyst components by hydrochloric treatment (step 1); immersing the hydrochloric acid-treated carbon nanotube in a mixed acid solution and sonicating the resulted solution (step 2); washing several times the surface of the sonicated carbon nanotube from step 2 with distilled water at room temperature under atmospheric pressure and filtered, leaving the resulting product standing at ambient temperature for 30-360 minutes and subjecting the resulted product to vacuum drying (step 3); and supporting metal catalyst nanoparticles on the inner channel of the carbon nanotube by CVD, while feeding a flow of metal precursors to the vacuum-dried carbon nanotube (step 4), wherein the heating process in step 1 for removing carbon impurities from the carbon nanotube catalyst is conducted in an oven heated to 450-550°C under air atmosphere for 30 minutes to 2 hours, and the treatment with hydrochloric acid is carried out by immersing the carbon nanotube in hydrochloric acid (6-10 mol), maintaining it therein for 6-24 hours, then washing with distilled water and drying in an oven at the temperature of 100-120°C for 12 to 24 hours, wherein the carbon nanotube treated with hydrochloric acid in step 2 is immersed in a mixed acid solution in which 14M nitric acid and 98% sulfuric acid are mixed at the mixing ratio of 1:1 by volume, and sonicated for 3-10 minutes, wherein the vacuum drying process in the step 3 is performed in an oven at the temperature of 100-120°C for 30 minutes to 2 hours, and wherein the metal catalyst nanoparticles supported on the carbon nanotube in step 4 include particles of platinum (Pt), ruthenium (Ru), nickel (Ni), cobalt (Co) or molybdenum (Mo), wherein the metal particles are provided in the form of metal precursors so as to be supported on the inner channel of the carbon nanotube, wherein platinum precursors are selected from the group consisting of methyltrimethylcyclopentadienyl-platinum (MeCpPtMe 3), Pt(Me) 3 (Cp), Pt(Tfacac) 2, Pt(Me) (Cp), Pt(Me) 2, [PtMe 3 (acac)] 2 (acac; acetylacetonato ligand), PtCl 2 2, Pt(PF 3) 4, Pt(acac) 2, and Pt(C 2 H 4) 3; ruthenium precursors include ruthenium acetylacetonate (Ru(acac) 3) or ruthenium carbonyl (Ru 5); nickel precursors include nickel nitrate (Ni(NO 3) 2) or nickel carbonyl (Ni 4); cobalt precursors include Co 3 NO; and molybdenum precursors include Mo 6.