The invention relates to the field of permanent magnets, in particular to a grain-boundary-diffusion heavy rare earth and neodymium iron boron magnetic material and a preparation method thereof. The grain-boundary-diffusion heavy rare earth and neodymium iron boron magnetic material comprises a magnetic material body and a surface coating adhered to the surface of the magnetic material body. The magnetic material body comprises, by weight, 4-6.2% of Pr, 18-25% of Nd, 0.8-1.5% of Dy, 0.8-2.8% of B, 2.2-4.2% of Cr, 0.1-0.4% of Al, 0.1-0.4% of Cu, 0.1-0.4% of Zr, and the balance Fe. The surface coating comprises an inner heavy rare earth layer and an outer anticorrosive layer. The grain-boundary-diffusion heavy rare earth and neodymium iron boron magnetic material has the advantages that residual magnetic induction intensity and magnetic energy product are not reduced while coercivity of a magnet is improved; high comprehensive magnetic performance and high corrosion resisting performanceare achieved.