The invention discloses sintered neodymium iron boron magnet steel which comprises, in weight percent, 27.5-30.5wt% of rare earth element R, 0.5-1.0wt% of Al, 0.03-0.06wt% of Pr, 0.03-0.06wt% of C, 0.35-0.5wt% of Cu, 0.08-0.12wt% of Nd, 0.2-0.4wt% of Ga, 0.2-0.5wt% of Pm, 0.6-1.2wt% of Co, 0.75-1.35wt% of B and the balance Fe. The rare earth element R is mixture of Ce, Ho, Sm, Dy and Tm, and the mixed weight ratio of Ce, Ho, Sm, Dy to Tm is 5:4:1:0.3:2. The invention further discloses a preparation method of the magnet steel. The preparation method is easy to operate, Ho and the rare earth elements such as Ce, Sm, Dy and Tm are added, part of expensive Nd and Pr is replaced, cost is reduced, corrosion resistance of the sintered neodymium iron boron magnet steel can be effectively improvedby adding Ho, weightlessness is reduced, Ce replaces Nd, eutectic temperature is reduced, so that sintering tempering temperature is reduced, cost is saved, and good performances are kept.