Magnesium alloys offer a lot of potential in the biomedical fields, due to their suitable elastic modulus for human bone, spontaneous degradability, and excellent biocompatibility, while low absolute tensile or yield strength and barren plastic abilities at room temperature significantly restrict their applications. As a successful method of enhancing mechanical properties, the hot deformation process can not only refine the grain sizes and broken sediments, but also introduce the high-density dislocations and change the texture orientation to improve the strength and plasticity. Based on the microstructure evolution laws, the latest research progress of Mg-based alloys under various hot deformation processes was reviewed. The differences in the deformation methods of rolling, forging, extrusion, and high-pressure torsion were compared. Under various hot deformation methods, the mechanism of grain refinement and the impact of dynamic recrystallization and dislocation propagation on the mechanical properties of Mg alloys were discussed. In addition, the relationships between microstructure and mechanical properties of hot-deformed Mg alloys were summarized.