The mechanism of the cogging torque generated in permanent magnet machines and some measures to reduce cogging torque were studied. Taking a rare earth type, permanent magnet synchronous motor with four poles, forty-eight slots, surface-mounted as an example, this paper analyzed the influence of pole arc coefficient, magnet pole displacement and adding supplementary slot on cogging torque in a two-dimensional finite element analysis method. The computed cogging torque values were compared with the experiment values of the sample machine, both of which agree with each other well. The research results have indicated that, with the appropriate choice of these methods, the cogging torque can be reduced effectively. 