The invention belongs to the technical field of catalysts, and particularly relates to a preparation method of a NiFe2O4 / Cu2O magnetic composite nanometer catalyst. According to the preparation method, nickel chloride hexahydrate, ferric trichloride hexahydrate, copper acetate hexahydrate, glucose, sodium hydroxide and deionized water are used as raw materials. The preparation method comprises the following steps: firstly preparing a mixed solution by using the nickel chloride hexahydrate and the ferric trichloride hexahydrate, then heating, separating, washing and drying the mixed solution to obtain a magnetic NiFe2O4 nanometer catalyst; secondly, dissolving copper acetate dihydrate in ethylene glycol monomethylether and stirring, adding NiFe2O4 solid powder to the mixed solution, stirring, adding the glucose, separating, washing and drying to obtain a NiFe2O4 / Cu2O magnetic composite nanometer catalyst. The NiFe2O4 / Cu2O magnetic composite nanometer catalyst can remove organic dyestuff in water through adsorption and photocatalysis efficiently and quickly, can be recycled through magnets and meanwhile has the characteristics of simple preparation and repeated use.