The borate family is the main source of deep-ultraviolet (DUV) birefringent crystals, and it has attracted a lot of attention due to versatile [B-O] basic units. Herein, two new borate-based compounds Na 6 Mg 3 B 10 O 18 F 6 and K 3 NaB 10 O 16 F 2 were discovered. Their fundamental building blocks are [B 5 O 11 ] and [B 5 O 10 F] units, respectively. The calculated results showed that the band gap and birefringence of K 3 NaB 10 O 16 F 2 ( E g = 6.93 eV, Δ n = 0.047 at 1064 nm) are greater than those of Na 6 Mg 3 B 10 O 18 F 6 ( E g = 5.40 eV, Δ n = 0.039 at 1064 nm). Furthermore, the effects of [B-O/F] units on band gap and birefringence were analyzed by the charge-transfer model and response electron distribution anisotropy method. The results show that introducing the [B-O/F] units can improve the band gap and birefringence. These findings will boost the exploration of DUV birefringent opticals.