Abstract: A DC UPS used in underground exchanger was designed. The UPS uses MAX713 to make intelligent charging for Ni-Cd battery; it takes MSP430F147 as microprocessor, uses external interruption mode to monitor working state of mine-used AC, and it can switchover to start Ni-Cd battery supply when mine-used AC has fault, so as to ensure continuous work of exchanger. The test result showed that the UPS has certain practicality.