DC uninterruptible power system and device thereof

A DC uninterruptible power system comprises a plurality of DC uninterruptible power devices which can be connected in series for standby. Each DC uninterruptible power device comprises a power line, a battery module which is electrically coupled with the power line for obtaining and storing electric power of a DC power supply, a voltage detection circuit which generates a first triggering signal when a fact that the voltage of the DC power supply is smaller than a first default value is detected, a current detection circuit which is used for generating a second triggering signal when a fact that the current of an adjacent DC uninterruptible power device that is electrically coupled with the power line is lower than a second default value is detected, a switch which is electrically coupled with the power line, and a control unit which controls the battery module according to the first triggering signal for outputting electric power to the power line, and controls the switch for connecting the power line with the current detection circuit according to the second triggering signal, thereby appropriately supplying power to the adjacent DC uninterruptible device.