The invention discloses a preparation method of a copper/cuprous oxide core-shell structure nanometer material. The method comprises the steps that soluble copper salt serves as a copper source, hydrazine hydrate serves as a reduction agent, cetyl trimethyl ammonium bromide (CTAB) serves as a surface active agent, and the copper/cuprous oxide core-shell structure nanometer material with copper nano particles as a core and cuprous oxide as a shell is prepared under the condition of the room temperature. The metal core-shell structure nanometer material prepared through the method can be used for the application research of the fields of photocatalysis, photoelectrocatalysis, solar cells and the like; and the preparation process is controllable, operation is easy, energy consumption is low, and stability is high.