In the present paper, the absorption spectra and their temperature-dependence of barium mateborate (β-BaB2O4) crpstals in the wavelength range of UV-VUV(50nm-350 nm)are reported. The characterises of the absorption spectra can be well explained with the theory of the indirect interband transition. The indirect absorption dege of this crystal is E0 = 6.24eV (at room temperature), and the average temperature coefficient of the indirect band gap is -6.5×10-4eV/K(288K-363K). The types and Debye temperatures of the phonons participating in the indirect transition have also been determined.