[Objective] Permanent magnet canned motor (PMCM) are widely used in petroleum, chemical, and nuclear industries due to their unique advantages. However, during operation, PMCM exhibit significant can losses, resulting in relatively low overall efficiency. This limitation substantially restricts their broader adoption and application, hindering technological progress and equipment upgrades in related industries. To address these challenges, this paper proposes an innovative sinusoidal air-gap magnetic flux density design method. [Methods] Through in-depth research and theoretical analysis, this study conducted a comprehensive optimization design of the permanent magnet parameters for a 1.5 kW PMCM using the proposed method, determining the optimal magnet dimensions. Additionally, finite element analysis was systematically employed to compare and analyze the performance of the PMCM before and after optimization. [Results] The research results demonstrated that the proposed design method can effectively reduce harmonic content in the air-gap magnetic flux density, significantly improving motor performance. After optimization, the motor losses were reduced by 30.44%, efficiency was increased by 8.87%, and the maximum operating temperature was lowered by 8.36%. [Conclusion] This research provides theoretical support for the widespread application of PMCM, facilitating the development of efficient and reliable motor equipment, thereby creating significant economic and social benefits.