The present invention provides a use for a blended alloy in the preparation of a neodymium-iron-boron magnet by using a waste sintered magnet, and further provides a method for preparing a neodymium-iron-boron magnet by using a waste sintered magnet. The present invention provides a blended alloy having a specific composition, which is used in the process of preparing a neodymium-iron-boron magnet from a waste sintered magnet. In the blended alloy having a specific composition, not only can the components and properties of the product be flexibly adjusted and configured to meet design requirements, the consistency of batch products be ensured, and the utilization rate of waste sintered magnets be improved, but the diffusion performance can also be facilitated for improvement. In the utilization method of the present invention, the waste magnet may be directly crushed into an alloy and blended with a rare earth-rich alloy without passing through smelting, so that the phase-rich defect of the waste magnetic steel is solved, and the magnetic performance is greatly improved; processing costs are reduced since no smelting is required; meanwhile, waste magnetic steel raw material may be 100% utilized without limitation on the smelting addition amount.