In the domain of control systems for permanent magnet synchronous motor (PMSM), the model sliding mode control method has gained significant prominence due to its formidable robustness and its ability to effectively counteract disturbances. Nevertheless, conventional sliding mode control approaches inherently employ an internal sign function, which manifests as oscillations in torque output within the control system, thereby adversely affecting both transient and steady-state performance. In response to this challenge, this research presents a piecewise model-free sliding mode control (PMFSMC) strategy specially tailored for PMSM. The conventional proportional integral sliding mode surfaces is replaced with piecewise sliding mode surfaces, mitigating the deleterious consequences of pronounced oscillations observed in traditional sliding mode control. Additionally, this paper proposes the integration of a reduced-order proportional-integral observer (ROPIO) to compensate for external disturbances, thereby augmenting the control system’s resilience against disturbances. Finally, the efficacy of this PMFSMC is substantiated through empirical validation.