The invention discloses a method for synthesizing a metal free catalyst self-assembled growing carbon nano-tube by chemical vapor deposition. The invention is characterized by firstly raising the temperature of a horizontal vacuum tube high temperature furnace into 940 to 980 DEG C and preserving the temperature under the protection of carries gases, then pumping the mixed gas of carbon source gas and the carries gases; the decomposing product of the carbon source gas is deposited on an underlay in the low temperature area of the high temperature furnace to form the self-assembled growing carbon nano-tube; the carbon source gas is gaseous compound containing carbon. The carrier gases are the mixed gas of one or two or a plurality of nitrogen, hydrogen or argon. As no metal catalysts are used, the carbon nano-tube prepared by the invention contains no metal catalysts, thus having the advantages of high output purity, low manufacture cost and being hopeful to realize continuous manufacture.