In the inverterpowered permanent magnet synchronous motor (PMSM), high frequency current time harmonics was produced by the high frequency switch tube, and the eddy current loss of permanent magnet (PM) was increased. Considering the current time harmonics in PM, an analytic equation about the eddy current loss was proposed. The relationship between the dimension of PM, penetration depth and eddy current loss was deduced in details. Then the conclusion was drawn. The eddy current loss of PM was greatest when the axial or circumferential dimension of PM was twice the penetration depth, and the accuracy of the conclusion was verified by an ideal 3D model. In addition, the eddy current loss simulation of a 48slot 8pole watercooled PMSM powered by an inverter was taken as an example. The results showed that a reasonable number of segments in PM could effectively reduce the eddy current loss.