Brushless doublyfed motor (BDFM) had promising application prospect in wind power generation. Coupling capability of rotor was an important factor affecting the power density and efficiency of the motor. Based on the analysis of structures of cage rotor, a segmented squirrelcage rotor was presented. At first, the topology of the BDFM and the principle of variablespeed constantfrequency (VSCF) generation were introduced. Secondly, analysis of BDFM with the above rotor structures was carried out using finite element software. Finally, the key parameters affecting the coupling capability were analyzed, such as spacing angle of rotor bars and layer number of rotor bars. The results showed that the new rotor structure held higher end space utilization ratio, higher motor power density and simple and reliable rotor structure under certain coupling capability.