Provided is a bridge cascade system, which includes at least one phase unit and a driving unit for the phase unit. The phase unit includes N bridge topologies cascaded on alternating current AC sides. The driving unit includes one driving power supply circuit, multiple bootstrap power supply circuits and 2N driving circuits. In the phase unit, the driving circuits are powered by the driving power supply circuit directly or through corresponding bootstrap power supply circuits. The driving circuits are configured to provide driving signals for corresponding switch transistors in the phase unit. In this way, one driving power supply is matched with multiple bootstrap power supply circuits, realizing power supply to the driving circuits corresponding to the switch transistors of all bridge topologies, which reduces the difficulty in designing the driving power supply for the bridge cascade system and reduces cost for the system.