The invention provides a dynamic direct-current voltage-stabilizing method for a static synchronous reactive compensation device. The method comprises the following steps: calculating a network voltage and an output voltage, obtained after a load reactive signal suddenly changes, of the static synchronous reactive compensation device, calculating an output current i(t), obtained after the reactive preset sudden change is output, of the static synchronous reactive compensation device, and selecting a switching point with the best capacitive and inductive characters. According to the dynamic direct-current voltage-stabilizing method for the static synchronous reactive compensation device, due to the fact that the output current is stabilized in the switching process, the symmetric performance and harmonic content of the output current of the static synchronous reactive compensation device are greatly improved, the dynamic performance of the static synchronous reactive compensation device is improved, the current of the static synchronous reactive compensation device is normally output in the switching process of the capacitive and inductive characters, the short-time over-current phenomenon can not occur, and the performance of the static synchronous reactive compensation device is improved.