To address the issues of low torque density, large torque ripple, and poor magnetic concentration effect in traditional radially magnetized surface-mounted permanent magnet motors, this paper utilizes the one-sided magnetic concentration effect of the three-segment Halbach permanent magnet array to enhance the motor’s air-gap magnetic density and optimize its electromagnetic performance. Firstly, a 2D finite element model of the motor is constructed to model the three-segment Halbach permanent magnet array. Secondly, through finite element simulation, the influence of changes in permanent magnet dimensions on the motor’s air-gap magnetic density and electromagnetic torque is comparatively analyzed. Finally, by comprehensively evaluating the variation laws of the above electromagnetic performance parameters, the permanent magnet dimensions are adjusted in a targeted manner to improve the motor’s electromagnetic performance, providing theoretical support for the design of high-power density motors.