The invention discloses a preparation method of a Mn3O4 nanowire or nanorod. The preparation method comprises the following steps: adding a divalent manganese salt and sodium acetate into low alcohol, and stirring to obtain a transparent liquid; preparing a Mn3O4 nanowire or nanorod from the liquid by adopting a solvothermal method; centrifugally separating and washing after the reaction to obtain the Mn3O4 nanowire or nanorod. According to the preparation method of the Mn3O4 nanowire or nanorod, the Mn3O4 nanowire or nanorod is synthesized by one step by utilizing the solvothermal method; and the Mn3O4 nanowire or nanorod with a needed slenderness ratio can be obtained in a controllable manner by changing the reaction conditions. The preparation method is simple in preparation process, efficient and low in raw material cost, and has significance in large-scale industrial production and practical application of the Mn3O4 nanowire or nanorod. The obtained Mn3O4 nanowire or nanorod is high in yield, high in purity, uniform in morphology and narrow in dimension distribution, has relatively good magnetism and is widely applied in catalysis, solar cells, heavy metal ion adsorption and the like.