The doubly-fed generator motor for variable speed pumped storage can maintain the active power output and then make full use of the power margin to become a stable reactive power source, so that it can flexibly participate in system voltage and phase regulation. In order to study the reactive power characteristics of the doubly-fed generator motor, based on the analysis of the relationship among the electrical quantities of doubly-fed generator motor, the V-curve of the doubly-fed generator motor for variable speed pumped storage is established on the basis of the stator current-rotor current, which can simply reflect the reactive power characteristics of the doubly-fed generator motor. Then, the variation law of V-curve of doubly-fed generator motor under different working conditions is studied. Finally, the hardware-in-loop test based on RTLAB platform shows that the doubly-fed variable speed pumped storage unit has the reactive power characteristics similar to synchronous motors, and also proves the correctness and effectiveness of the proposed analysis method.