An uninterruptible power supply system, wherein the system comprises a load, an active battery power supply system, and a standby battery power supply system, wherein: the active battery power supply system comprises an active battery pack and a first control system, and the standby battery power supply system comprises a standby battery pack and a second control system, wherein the first control system controls the active battery pack to supply power to the load, and the second control system controls the standby battery pack to supply power to the load; and the first control system and the second control system form interlocking control, so as to control that only the active battery pack or only the standby battery pack supplies power to the load at a certain moment; wherein the active battery power supply system further comprises a first unidirectional discharge circuit, and the standby battery power supply system further comprises a second unidirectional discharge circuit, and an output end of the active battery pack is connected to an input end of the first unidirectional discharge circuit, an output end of the first unidirectional discharge circuit is connected to one end of the load and an output end of the second unidirectional discharge circuit, an input end of the second unidirectional discharge circuit is connected to an output end of the standby battery pack, and another output end of the active battery pack is connected to another end of the load and another output end of the standby battery pack, characterized in that a discharge cutoff voltage of the active battery pack is greater than a discharge startup voltage of the standby battery pack, wherein the active battery pack and the standby battery pack are both formed by N electrochemical cells connected in series, the number of unidirectional discharge components disposed in the first unidirectional discharge circuit is greater than the number of unidirectional discharge components disposed in the second unidirectional discharge circuit, and N is a natural number, wherein the unidirectional discharge component is a silicon controlled rectifier or an insulated gate bipolar transistor. the active battery power supply system comprises an active battery pack and a first control system, and the standby battery power supply system comprises a standby battery pack and a second control system, wherein the first control system controls the active battery pack to supply power to the load, and the second control system controls the standby battery pack to supply power to the load; and the first control system and the second control system form interlocking control, so as to control that only the active battery pack or only the standby battery pack supplies power to the load at a certain moment; wherein the active battery power supply system further comprises a first unidirectional discharge circuit, and the standby battery power supply system further comprises a second unidirectional discharge circuit, and an output end of the active battery pack is connected to an input end of the first unidirectional discharge circuit, an output end of the first unidirectional discharge circuit is connected to one end of the load and an output end of the second unidirectional discharge circuit, an input end of the second unidirectional discharge circuit is connected to an output end of the standby battery pack, and another output end of the active battery pack is connected to another end of the load and another output end of the standby battery pack, characterized in that a discharge cutoff voltage of the active battery pack is greater than a discharge startup voltage of the standby battery pack, wherein the active battery pack and the standby battery pack are both formed by N electrochemical cells connected in series, the number of unidirectional discharge components disposed in the first unidirectional discharge circuit is greater than the number of unidirectional discharge components disposed in the second unidirectional discharge circuit, and N is a natural number, wherein the unidirectional discharge component is a silicon controlled rectifier or an insulated gate bipolar transistor.