The invention discloses a high-power low-frequency oscillation test power supply device capable of testing the control performance and the low-frequency oscillation suppression functions of devices of a dynamic reactive power compensation device, a grid-connected converter and the like under a working condition of low frequency oscillation. The high-power low-frequency oscillation test power supply device is connected to a power network in parallel, and constant DC side voltage and constant reactive power control at a rectifier side is achieved through sampling network voltage and rectifying valve side current and DC side voltage; an inverter side carries out constant AC side voltage and frequency control through sampling output voltage of a power supply as a feedback input signal of a controller; and meanwhile, low-frequency voltage of the power network is controlled by adopting a voltage closed-loop, thereby achieving the low-frequency oscillation generator function of the network voltage.