Rationally designing a high‐performance nonlinear optical (NLO) crystal remains a great ongoing challenge. It involves not only the design of noncentrosymmetric structures but also property optimization. In this communication, a new strategy for effectively designing the NLO crystal has been put forward, that is, using the structure‐directing property of oxyfluoride anions to obtain a noncentrosymmetric and polar structure, and then by substitution of IO3− for isovalent F− anions to further enhance the SHG response. With this strategy, a new iodate fluoride, Ba2[MoO3F(IO3)](MoO3F2) has been successfully designed from the Ba2(MoO3F2)F2 with the cis‐directing [MoO4F2]4− groups. It exhibits a large SHG response (≈8×KDP), a wide transparent region (0.30–10.92 μm), a high laser‐induced damage threshold (LDT) (88.53 MW cm−2), and a large birefringence (≈0.264@532 nm). These indicate Ba2[MoO3F(IO3)](MoO3F2) would be a promising NLO crystal.