The present invention relates to a barium tetraborate compound and a barium tetraborate non-linear optical crystal, and a preparation method and use thereof, wherein the chemical formulae of the barium tetraborate compound and the non-linear optical crystal thereof are both BaB4O7, with a molecular weight of 292.58; the barium tetraborate non-linear optical crystal has a non-centrosymmetric structure, which belongs to a hexagonal system, and has a space group P65 and lattice parameters of a=6.7233(6) Å, c=18.776(4) Å, V=735.01(17) Å3, and Z=6, wherein the powder frequency-doubled effect thereof is two times that of KDP (KH2PO4), and the ultraviolet cut-off edge is lower than 170 nm. The barium tetraborate compound is synthesised by a solid-phase reaction method; the barium tetraborate non-linear optical crystal is grown by a high-temperature molten solution method; and the crystal has a moderate mechanical hardness, is easy to cut, polish and store, and is widely applicable in the non-linear optics of a double-frequency doubling generator, an upper frequency converter, a lower frequency converter or an optical parameter oscillator etc.