A new polyborate Sr3BeB6O13 has been synthesized and grown by the traditional solid-state reaction method and spontaneous crystallization flux method. It crystallizes in orthorhombic space group Pnma (No. 62) with the following unit cell dimensions: a = 12.775(3) Å, b = 10.029(2) Å, c = 8.0453(16) Å, and Z = 4. The crystal is characterized by an infinite two-dimensional network with a tri-six-membered ring (BeB5O13)(9-) anionic group, which was first found in beryllium borates. Ultraviolet (UV)-visible-near-infrared diffuse reflectance spectroscopy demonstrates that its UV cutoff edge is below 200 nm, and the first-principles electronic structure calculations reveal its energy band gap of 7.03 eV (∼175 nm). Thermal analysis exposes its incongruent feature at 1043 °C. IR spectroscopy measurements are consistent with the crystallographic study. These data reveal that this crystal would be applied as a deep-ultraviolet optical material.