The utility model discloses a battery pack monitoring device used for a transformer station DC system. The battery pack monitoring device comprises a battery pack which is composed of multiple single-body batteries, and single-body battery discharge units which are corresponding to the single-body batteries in number. The battery pack is respectively connected with a charging device and a load. The single-body battery discharge units are connected in parallel between the two ends of the corresponding single-body batteries. The single-body battery discharge units comprise a voltage acquisition comparison circuit, a first-stage discharge switch circuit, a current divider, a second-stage discharge switch circuit, a voltage comparison circuit and a current comparison circuit. The current divider is respectively connected with the first-stage discharge switch circuit, the second-stage discharge switch circuit, the voltage comparison circuit, the current comparison circuit and the single-body batteries. The voltage acquisition comparison circuit is respectively connected with the single-body batteries and the first-stage discharge switch circuit. The second-stage discharge switch circuit is also respectively connected with the voltage comparison circuit and the current comparison circuit. Power can be supplied to the DC load by the battery pack monitoring device in any cases.