SmCo₁₂, with its large magnetic energy product, is a highly promising high-temperature permanent magnet that has attracted significant attention. However, the widely existing ThMn₁₂-type crystal structure in this system faces serious stability problem, which significantly hinders its practical engineering applications. Exploring a novel SmCo₁₂ structure that combines stability and excellent magnetic properties is crucial for breaking through this bottleneck. In this study, the metastable phases of the SmCo₁₂ system are systematically investigated by using a local particle swarm optimization algorithm combined with first-principles calculations. The theoretical calculations reveal a hexagonal phase structure (space group P\overline31m ) with a formation energy 90 meV/atom lower than that of the conventional ThMn₁₂-type SmCo₁₂. Its phonon spectrum shows no imaginary frequencies and its structure remains stable during Nosé-Hoover thermostat simulations at 1200 K, confirming its dynamic stability and thermodynamic stability. The electronic structure reveals that this structure exhibits metallic characteristics, with a total magnetic moment of as high as 21.81 μ_B/f.u. and a magnetocrystalline anisotropy constant of up to 11.10 MJ/m³, significantly exceeding similar high-cobalt-content Sm-Co systems. Furthermore, theoretical predictions indicate that the hexagonal phase SmCo₁₂ structure exhibits exceptionally outstanding magnetic properties, with maximum energy product, anisotropy field, and Curie temperature reaching 54.56 MGOe, 15.01 MA/m, and 1180 K, respectively. The newly discovered hexagonal SmCo₁₂ phase provides a novel direction for solving the stability problem of the ThMn₁₂-type structure.