The invention relates to a nanosheet self-assembled submicron flower-like M phase vanadium dioxide powder and a preparation method thereof. The nanosheet self-assembled submicron flower-like vanadiumdioxide powder with high purity is synthesized by a one-step low-temperature hydrothermal method. The method is simple in reaction process, low in temperature, and easy to control and does not need large equipment and harsh reaction conditions. When the above product is used as an anode material for a lithium ion battery and an oxygen generation electrocatalyst, the product can show excellent electrochemical performance and electrocatalytic performance. The nanosheet self-assembled submicron flower-like M phase vanadium dioxide powder prepared by the preparation method according to the invention is composed of submicron flowers with a uniform diameter of about 1 mu m, the submicron flowers are partially gathered, the submicron flowers are assembled by nanosheets with a thickness of about 10 nm in an intercalation way, and the nanosheet shows the (011) crystal plane orientation growth characteristic.