Fluorooxoborates, benefiting from the large optical band gap, high anisotropy, and ever-greater possibility to form non-centrosymmetric structures activated by the large polarization of [BOxF4-x]((x+1)-) building blocks, have been considered as the new fertile fields for searching the ultraviolet (UV) and deep-UV nonlinear optical (NLO) materials. Herein, we report the first asymmetric alkaline-earth metal fluorooxoborate SrB5O7F3, which is rationally designed by taking the classic Sr2Be2B2O7 (SBBO) as a maternal structure. Its [B5O9F3](6-) fundamental building block with near-planar configuration composed by two edge-sharing [B3O6F2](5-) rings in SrB5O7F3 has not been reported in any other borates. Solid state F-19 and B-11 magic-angle spinning NMR spectroscopy verifies the presence of covalent B-F bonds in SrB5O7F3. Property characterizations reveal that SrB5O7F3 possesses the optical properties required for deep-UV NLO applications, which make SrB5O7F3 a promising crystal that could produce deep-UV coherent light by the direct SHG process.