The invention relates to the technical field of nonferrous metallurgy chemistry, and discloses a technological method and a device for copper and molybdenum separation waste water cyclic utilization. According to the method, overflow water and filtering water in the copper and molybdenum separation process are intensively collected in a return water tank by an overflow water pipe and a filtering water pipe; flotation reagents in the return water tank are absorbed by adding activated carbon so as to remove residual reagents disadvantageous to copper and molybdenum separation and enable return water to become return water which is rich in sodium sulphide and beneficial to copper inhibition and molybdenum flotation; and a water pump beside the return water tank is used for pressing the processed return water into the return pipe, so that the return water can return to separating flotation operation for cyclic utilization. According to the invention, the use level of the sodium sulphide is remarkably reduced; meanwhile, the treatment pressure on mine sewage can be effectively relieved; energy conservation and emission reduction are realized; the environmental pollution is small; and excellent economic and social benefits are realized.