This paper is researching about the design of abnormal monitoring module of a military special vehicle power supply system,which is supplied power by accumulator. It provides reference data for system control terminals when analyzing and removing failures. Monitoring module uses the microcontroller C8051F040 as the control core. It records abnormal voltage beyond the normal range when monitoring the "system DC26V" and "system DC5V" power supply. And it sends abnormal data to system control terminals by RS-485 communication mode . The module is small volume ,fast acquisition speed ,recording time marks and stable operation.Through the actual application it proved that the monitoring module can precisely record various power abnormalities during operation.