In this paper, for a brushless doubly-fed machine based on differential modulation, it is found that there is a significant difference in the induced current in the rotor of the brushless doubly-fed machine with different pole-pair combinations of the control and power windings, and it will have an effect on the power density of the brushless doubly-fed machine. In order to study the difference of rotor currents in brushless doubly-fed machines with different pole-pair combinations, the relationship between rotor cur-rents and machine parameters are analyzed and calculated by taking a 1/4-pair pole combination of differentially-modulated brushless doubly-fed machine as an example. On this basis, the steady state temperature rises of the differential modulated brushless doubly-fed machine was analyzed and predicted under different pole-pair combinations. Finally, at the temperature rise level, the opinions on the selection of the pole pair numbers of the control winding and power winding of the brushless doubly-fed machine are given. The results of this paper provide a reference for the study of the influence of rotor current of wire-wound brushless doubly-fed machine and pole-pair number selection on the power density of the machine.