The utility model relates to an apparatus for replacing a fault accumulator of an accumulator battery during operation in an electric uninterrupted state. The utility model comprises an electrode judging circuit 1, a first replacement circuit 2 and a second replacement circuit 3, wherein the electrode judging circuit 1 is connected to both ends of a fault accumulator 5 in parallel to judge the polarity of the fault accumulator; the first replacement circuit 2 is connected with the electrode judging circuit 1 in parallel through a switch K2, when the electrode judging circuit 1 judges that the polarity of the fault accumulator 5 is correct, the first replacement circuit 2 replaces the fault accumulator 5 to work; the second replacement circuit 3 is connected with the electrode judging circuit 1 in parallel through a switch K1, when the first replacement circuit 2 does not work, the second replacement circuit 2 replaces the fault accumulator 5 to work. The apparatus can be overhauled without changing the operating mode of a direct current system or shutting down a recloser, and does not affect the accumulator battery to supply power for a control bus, so that the safety coefficient in overhauling process is enhanced. The utility model has the advantages of convenient operation and small volume.