The invention relates to a sodium fluoborate compound, a sodium fluoborate birefringent crystal as well as a preparation method and an application. The compound has the chemical formula of Na2B6O9F2 and molecular weight of 292.84 and is prepared with a solid phase method. The sodium fluoborate birefringent crystal has the chemical formula of Na2B6O9F2 and molecular weight of 292.84 and belongs toa monoclinic system, the space group is P21 / c and the cell parameters are a=8.1964(12) angstrom, b=13.0005(19) angstrom, c=7.8955(11) angstrom, Z=4 and V=841.3(2) angstrom<3>, and the crystal is grownwith a flux method. The crystal is the birefringent crystal having centimeter-level large size and belonging to the monoclinic system, has birefringence of 0.080 at 589.3 nm and ultraviolet transmitting waveband cut-off edge of 169 nm and is suitable for the birefringent crystal. The crystal has the advantages that the operation is simple, the cost is low, used reagents are inorganic raw materials, the toxicity is low, the growth cycle is short, physical and chemical properties are stable and the like in the growth process. The crystal has important applications in preparation of Glan prisms,Wollaston prisms, Rochon prisms or polarizing beam splitter prisms, optoisolators, circulators and beam displacers.