The invention discloses a nano-carbon fiber preparation method and equipment, which aims to improve yield of carbon fibers. The preparation method includes heating the inside of a vertically arranged tubular reaction cavity, filling gas 1 and catalyst from the upper side of a furnace, feeding gas 2 from the lower side of the furnace, and obtaining nano-carbon fibers. The gas 1 is gas of a carbon source and carrier gas, and the gas 2 is nitrogen or hydrogen. The preparation equipment is the vertical tubular sealed reaction cavity, a first gas inlet pipe and a catalyst inlet pipe are arranged on the upper portion of the reaction cavity, a second gas inlet pipe is disposed on the lower portion of the reaction cavity, and a heating resistance wire is arranged on the periphery of the reaction cavity. Compared with the prior art, the preparation method adopts the vertically arranged tubular sealed reaction cavity, a mode that the gases are vertically guided into the cavity from different directions is adopted, the carbon source and the catalyst are sufficiently reacted and deposited under the action of fluid, yield of gas-phase deposited carbon fibers is improved under the condition that the reaction cavity is not large, and industrialization of nano-carbon fiber production is promoted.