Different crystal structures of CrB were obtained bythe CALYPSO software. The electronic structure and mechanical properties of CrB were analyzed through first-principles calculations. The results show that the structure of CrB transits from α-CrB to β-CrB phase at 90 GPa. The β-CrB phase exhibits both covalent and ionic bonds, while α-CrB phase is dominated by ionic bonds. The modulus and hardness of both phases increase with increasing pressure. However, the hardness of β-CrB is less than that of α-CrB, indicating that the comprehensive mechanical properties of CrB are optimized at 90 GPa. From the perspective of electronic structure, the reasons for the changes in the mechanical properties of CrB under different pressures were explained.