To improve the electromagnetic performance of the built-in U-type permanent magnet synchronous motor and suppress the low-frequency vibration and noise of the motor, a motor topology is proposed with a U-type pole structure combined with the Halbach magnetizing method and rotor slotting. Firstly, the relevant electromagnetic performance expressions of the motor are derived, and the low-frequency vibration and noise fluctuation composition of the radial magnetic flux density and radial electromagnetic force density between the stator and rotor are analyzed. Next, using analytical and finite element methods, the spatial and temporal distribution of the radial electromagnetic force in the air gap is obtained. Parameter sensitivity analysis, parameter scanning method, and response surface method are used to multi-objective optimization of the selected rotor topology parameters to obtain the optimal parameter solutions. Finally, no-load reaction potential, radial flux density, cogging torque, output torque, torque pulsation, radial electromagnetic force density, vibration acceleration and sound pressure level of the U-type pole structure are compared and analyzed with four other U-type pole structures. The U-type motor structure is validated by combining electromagnetic, mechanical and acoustic fields analyses. The results show that by adding a type I magnetic pole to the U-type magnetic pole structure, changing the magnetizing method, and modulating the sinusoidal degree of the air gap magnetic field by dq-axis slotting, the motor’s cogging torque decreased by 91.3%, the no-load reverse potential is increased by 53 V, the output torque is increased by 39.6%, the amplitude of radial electromagnetic force waves in the air gap decreased at all harmonic orders, the vibration acceleration of the stator assembly decreased significantly at all frequencies, and the maximum sound pressure level around the motor decreased by 9 dB at the peak, with a reduction rate of 10.1%.