A technology for preparing nano-metallic oxide powder with a DC (direct-current) plasma method comprises steps as follows: a high-purity metal block is put into a smelting furnace and is melted, and a melt delivery tube connected with the smelting furnace is heated; a reaction chamber is subjected to vacuum pumping until the pressure reaches 2-10 MPa, cooling air is introduced into the reaction chamber, and cooling water is introduced into a reactor interlayer arranged in the reaction chamber; an arc plasma gasification system power source of a reactor is switched on, gasification current is adjusted to 10-2,000 A, and voltage is adjusted to 5-400 V; inert gas is introduced into the metal melt, the melt delivery tube is adopted for flow guidance, the gasification reaction is performed, and metal jet is formed; the metal jet is gasified under the action of arc plasma so as to form atomic clusters, the atomic clusters are subjected to a reaction with oxygen, oxide nanoparticles are formed, is condensed under cold-air negative pressure and enters a powder collecting chamber with cold air flow, and the nano-metallic oxide powder is obtained. The technology is simple, does not need a plasma source and has high yield, and the prepared nano-metallic oxide powder is not prone to agglomeration, is high in purity and facilitates large-scale production.