Nonlinear optical (NLO) materials are significant for their crucial role in the development of modern optoelectronic and laser technology. Recently, fluorooxoborates have aroused the widespread attention for their tight relationship between the micro-properties of functional [BOxF4–x](x+1)– (x = 0, 1, 2, and 3) modules and macroscopic performances. Nevertheless, whether fluorooxoborates with the anionic groups only composed of condensed [BO2F2] units exhibit a strong second harmonic generation (SHG) response remains unclear. Here, eight possible synthetic structures with the [BOF2]∞ chain in the CaB2O2F4 system were predicted by using evolutionary algorithm crystal structure prediction techniques. Among them, CaB2O2F4-I, II, IV, and V are centrosymmetric and CaB2O2F4-III, VI, VII, and VIII are non-centrosymmetric structures. Hence, CaB2O2F4-VI (C2) possesses an extremely short ultraviolet cutoff edge (147 nm) and the largest SHG coefficient among reported non-centrosymmetric fluorooxoborates only consisting of the [BO2F2] group. Also, the origin of the SHG coefficient was analyzed in detail through theoretical calculation.