A system and method for producing carbon nano-structures. The proposed method allows for producing carbon nano-structures on a commercial scale, while reducing the degree of agglomeration and the influence of the walls of the reaction chamber on the process, as well as increasing control over the process of preparation of the nano-structures. A method for producing carbon nano-structure by decomposition of hydrocarbon gases in the reaction chamber in the presence of a catalyst includes preparing a working mixture, wherein the mixture includes nano-particles comprising a catalyst substance, a carrier gas and gaseous hydrocarbons; feeding the reaction mixture into the reaction chamber; discharging carbon nano-structures from the reaction chamber in a stream of gaseous products of hydrocarbon decomposition; and separating carbon nano-structures from gaseous products of hydrocarbon decomposition.