External rotor permanent magnet synchronous motor (PMSM) as in-wheel motor is widely used in electric vehicles, but there are few studies on in-wheel motor vibration and noise. An in-wheel motor with the rated power of 10 kW and the rated speed of 500 r/min is taken as an example to calculate the radial electromagnetic force density and vibration and noise characteristics of the motor in finite element simulation by constructing 2D finite element model of the in-wheel motor. The vibration and noise characteristics of the external rotor in-wheel motor are studied from pole arc coefficient and auxiliary slots on stator teeth. It is shown in simulation that the vibration and noise characteristics of the in-wheel motor are better when the pole arc coefficient is about 0.72 and double auxiliary slots are set on the stator teeth tip.