This paper investigates the vibration characteristics of the rotor system of permanent magnet synchronous motor with air-gap eccentricity. A dynamic model of the rotor system is built. According to the distribution of magnetic flux density generated by permanent magnet and armature current under load, Unbalanced Magnet Pull (UMP) is calculated with the Maxwell stress tensor and is substituted into the dynamic model. From several illustrating numerical examples, the effects of different eccentricities and loads on rotor vibration are discussed in detail. The results show that, the mass unbalance weakens the effect of the UMP while aggravates the vibration of the rotor, the magnitude and orientation of the initial eccentricity can also change the vibration characteristic of the rotor, and the vibration will be weakened when the orientation of initial eccentricity is close to the direction of the gravity. As the load changes, the corresponding vibration components will be excited with the same frequencies as those of the load.