Electromagnetic vibration and noise level is a comprehensive index to measure the comfort of electric vehicles. Radial electromagnetic force is the main excitation source of vibration and noise. The radial electromagnetic force of permanent magnet synchronous motor (PMSM) is analyzed. The three-dimensional spectrum obtained from the radial electromagnetic force space-time separation is used to extract the certain time-space order and the corresponding force densities which have great influence on the electromagnetic noise. The finite element method is used to simulate the vibration and noise of PMSMs with different types of step-skewed rotor. The optimal type of step-skewed rotor is found by comparing the results.