The invention discloses a preparation method of a sintered neodymium-iron-boron magnet with high magnetic energy product and high coercivity. The method comprises the steps that firstly, a sintered neodymium-iron-boron rough magnet is prepared through the processes of batching, melting stripping, hydrogen explosion, air milling, magnetic field molding, sintering and machining; then pretreatment steps including derusting, degreasing, pickling and cleaning are carried out on the rough magnet; the rough magnet is sprayed and coated with a prepared heavy rare earth suspension; and finally spark plasma diffusion treatment (SPS) and tempering heat treatment are carried out on the magnet sprayed with the heavy rare earth adhesion layer to acquire the sintered neodymium-iron-boron magnet. Compared with the prior art, the preparation method provided by the invention has the advantages of excellent utilization of heavy rare earth, high processing efficiency, low production cost, high magneticproperty consistency and the like, is easy to realize commercial applications, can well meet customer needs, and is suitable for preparing the low-costed sintered neodymium-iron-boron magnet with highmagnetic energy product and high coercivity.