Disclosed herein is a direct current (DC) uninterruptible power supply system. The DC uninterruptible power supply system is connected to a DC power conversion system converting prevailing alternating current (AC) power into DC power, supplies the DC power to a load, charges an internal auxiliary power supply device with the DC power, and continuously supplies power to the load from the auxiliary power supply device while cutting off an electric connection with the DC power conversion system when the DC power conversion system short-circuits due to a leakage current or damage thereof or is disconnected.