The invention relates to a preparation method of a nitride-boride fluorescent powder material. The preparation method is characterized in that common metal salt or oxide is used as the raw material, a high-temperature solid-phase method is used for preparation, the preparation process of nitride fluorescent powder is simplified, and production cost is lowered. The expression of the nitride-boride fluorescent powder material is AM4-4x(BN2):xD, wherein A is one or more of Li, Na, K, Rb and Cs; M is one or more of Mg, Ca, Sr and Ba, and D is one or more of Mn<2+>, Ce<3+>, Pr<3+>, Nd<3+>, Pm<3+>, Sm<3+>, Sm<2+>, Eu<3+>, Eu<2+>, Tb<3+>, Dy<3+>, Ho<3+>, Er<3+>, Tm<3+>, Yb<3+> and Yb<2+>. The preparation method specifically includes: weighing the raw materials of A, M and D and boric acid according to stoichiometric ratio, adding appropriate amount of acetone into the raw materials, and sufficiently grinding to obtain a mixture; performing heat preservation on the mixture for 1-5 hours in an environment of 400-650 DEG C and under reduction atmosphere; grinding and evenly mixing obtained preliminary-combustion substance, and performing heat preservation on the mixture for 1-8 hours in an environment of 700-900 DEG C to obtain the nitride-boride fluorescent powder material. The preparation method has the advantages that the method using a solid-phase synthesizing method is low in synthesizing temperature, simple in preparation process, low in cost, safe, reliable, short in production cycle and suitable for large-scale industrial production, and the prepared fluorescent powder is excellent in light-emitting efficiency.