Abstract: Permanent Magnet Synchronous Motor (PMSM) have gained widespread attention in the rail transit field due to their supreme performance. This study systematically reviews the applications of PMSM in rail transit, with a focus on the design of built-in rotor structures. Research indicates that this structure significantly enhances power density and improves the demagnetization resistance of permanent magnets through magnetic circuit distribution. Based on the shape of permanent magnets, the application scopes of four built-in PMSM rotor topologies are comparatively analyzed, elucidating their technical advantages and limitations in suppressing leakage flux and reducing eddy current losses. Combining the magnetic circuit characteristics of PMSM, optimization strategies for air-gap magnetic field waveforms are summarized to mitigate torque ripple issues. Additionally, current research trends and development directions in PMSM control technology are discussed from perspectives such as vector control algorithm improvements and multi-physics coupled modeling. The study highlights that back-EMF suppression and thermal demagnetization protection of permanent magnets are key challenges restricting the large-scale application of PMSM. Future efforts should focus on optimizing PMSM rotor structures, addressing magnetic performance degradation of permanent magnet materials, planning optimal current trajectories under dynamic parameter coupling, and intelligent demagnetization monitoring system development, to promote deeper adaptation and performance breakthroughs of permanent magnet traction motors in the rail transit field.