The invention provides a preparation method of vanadium tetrasulfide nano-powder and an application. The method comprises the following steps: firstly, mixing a vanadium source solution with a sulfur source solution, stirring the mixture until semi-clear and then adding an acid or alkali solution to adjust the pH of a reaction liquid; transferring the reaction liquid to a homogeneous reaction instruction for hydrothermal reaction; and finally cooling the reacted product and then washing, collecting and drying the product to obtain the vanadium tetrasulfide nano-powder. According to the method, the technology is is simple and easy to control; and the prepared vanadium tetrasulfide nano-powder is uniform in chemical composition and relatively high in purity, and demonstrates excellent electrochemical properties when used as an electrode material for a lithium/sodium-ion battery. Furthermore, the disadvantage of a high temperature of a traditional calcination method is overcome; large equipment and harsh reaction conditions are not needed; and the method is cheap and available in raw material, low in cost, high in productivity, free of after-treatment and friendly to environment, and can be suitable for large-scale production.