Based on the fact that the actual inductance and capacity are essentially of fractional- order,this paper establishes a fractional- order model of the permanent magnet synchronous motor (PMSM).Then,the pseudoran-dom binary sequence is taken as the external excitation signal of the PMSM to implement an identification experi-ment.Based on the experimental data,the fractional- order model is identified by using the output- error identifica-tion algorithm.Finally,according to the same criteria,two PI controllers are designed respectively for the identified fractional- order model and the traditional integer- order one.From the comparative experiment of the two PI contro-llers,it is found that in terms of accuracy,the proposed fractional- order model is superior to the traditional integer-order one in describing the PMSM.