An uninterruptible power system is provided. When a first power supply of the system is faulty, in a process in which a switch unit switches power supply from the first power supply to a second power supply, the second power supply discharges to a direct current bus using a bidirectional power converter, electric energy stored in the direct current bus is also discharged in a short time in a process of the switch, and the direct current bus outputs both a discharging current of the second power supply and a discharging current of the direct current bus to a system output end, which ensures that the direct current bus outputs a stable voltage in a gap period of an action of the switch unit.