Direct-current uninterruptible power system and abnormal voltage detection method thereof

The invention discloses a direct-current uninterruptible power system. The direct-current uninterruptible power system comprises a multiplexer, a battery unit, a linear voltage stabilizer, a switching transistor, a voltage comparator and a microcontroller. The multiplexer receives a first control signal, a first reference voltage and a second reference voltage and outputs a control voltage according to the first control signal. The switching transistor is provided with a body diode which has a break-over voltage. When the direct-current uninterruptible power system is in a non-discharge mode, the switching transistor is in a cut-off state, and the linear voltage stabilizer receives the first reference voltage, so that a voltage obtained through subtraction between an output voltage and a supply voltage is smaller than the break-over voltage, and then the body diode is cut off.