The introduction of fluorine (F) into the borate crystals is proven to be an effective approach in designing novel non-centrosymmetric crystals, which is a requirement for nonlinear optical (NLO) materials. In this contribution, the electronic structure and optical properties of borate fluoride crystals are determined by the first-principles method. First-principles calculations indicate that the key second-harmonic generation (SHG) factor is attributed not only to borate groups but also to the bonding of the F anions with cations where F coordinates to cations (Sr, Ba). The electron withdrawing effect of the F atom leads to the higher values for anisotropy of the polarizability around cation-centered polyhedra, ultimately making it easy for the external electric field of incident light to effect the dielectric susceptibility. The direct contribution of anion on the NLO properties is observed as fluorine-induced variation of electronic structure.