Considering the difficulty to calculate rotor losses accurately by loss model and too much time by threedimensional finite element method, the rotor loss of a 36 slots 42 poles singlelayer surface permanent magnet synchronous motor with fractionalslot concentrated winding was calculated based on the twodimensional motion transient finite element method operating at maximum torque both in constant torque region and in fluxweakening region. Additionally, the effects of the number of axial segments, slot width and air gap thickness on the loss of permanent magnets at high speed were investigated. It was shown that the magnet loss accounted for more than 90% of the total rotor loss in the whole speed range, the hysteresis loss of the rotor core was higher than the eddy current loss when the speed was lower than 1 500 r/min, and the eddy current loss was obviously higher than the hysteresis loss when the speed was higher than 1 500 r/min. The eddy current loss of the magnet could be reduced obviously by segmenting the permanent magnet; changing slot width contributed nothing to magnet loss under load condition;increasing the air gap width had no obvious effect on reducing the loss of permanent magnet. Meanwhile, changing the slot width and the thickness of the air gap would change the inductance and affect the performance of the motor.