Low-speed high-torque transmission systems are widely employed in applications such as mining equipment and marine propulsion. However, the commonly used drive method, combining a conventional-speed induction motor with a reduction gearbox, results in increased system size, higher maintenance costs, and reduced reliability and operational efficiency. These limitations hinder its further development and broader application. As a result, direct-drive technology has emerged as the developmental trend and inevitable choice for low-speed high-torque transmission systems. The permanent magnet synchronous motor (PMSM) is particularly well-suited for low-speed direct drive applications due to its straightforward design, exceptional reliability, high efficiency, and excellent power factor. Domestic and international literature on the development history and fundamental structural features of low-speed high-torque permanent magnet direct-drive motors (LHPMDMs) is reviewed. In-depth research has addressed several persistent issues in LHPMDMs, including large volume, insufficient torque stability, high production costs, air gap eccentricity, and demagnetization. To tackle these challenges, solutions are proposed through new topologies, novel processes, advanced cooling systems, parameter optimization techniques, and online detection technology. Furthermore, the practical application and promotion of LHPMDMs are summarized. Finally, based on the current state of research, unresolved challenges and potential future development directions for LHPMDMs are discussed prospectively.