The invention discloses a hydro-thermal synthesis method of a rod-shaped nanometer zinc oxide, which belongs to the field of inorganic non-metal materials, and comprises the steps: soluble zinc salt such as zinc acetate is dissolved in water and added with an appropriate amount of benzoic acid to be taken as an auxiliary agent, NaOH solution is used for regulating the pH value to be 12-14, and precipitate and the solution are heated in a high-pressure autoclave for the growth of the nanometer zinc oxide. The heating mode can be microwave heating or resistance wire heating, and the outgrown structure is the zinc oxide consisting of nanometer rods. The method has the advantages of simple technology and low cost, and uses the benzoic acid as the auxiliary agent for controlling the appearance and the size of zinc oxide crystal.