The invention relates to a small autonomous underwater robot (hereinafter referred to as AUV) power management system. A power control circuit is connected with a power distribution circuit and a battery pack. The power control circuit is used to perform AUV power distribution and can be used to monitor the real-time current of the whole AUV; the power control circuit is in communication with a central control system through a CAN interface; and the power control circuit can be connected with an external umbilical cable and used to charge the battery pack when the AUV is ashore. The power distribution circuit is used to convert the voltage outputted by the power control circuit and supply the converted voltage to the central control system and a propulsion system. The battery pack is the main power source in the power management system for supplying power to the power control circuit. The system of the invention is used to manage the energy utilization of the self-provided battery pack of the small AUV when the small AUV is in underwater operation, and at the same time, the small AUV can be switched to the charging mode when the small AUV is connected with the umbilical cable on the surface of the water, and a umbilical power source is used to supply power to the system.