The land Grid transmits continuous electrical power to ocean cabled observatory through optic-electric hybrid cables and junction boxes. A power management and control system is designed for ocean cabled observatories. It also helps to implement online real time monitoring and increase the reliability and efficiency of the undersea power supplement for scientific instruments. By measuring temperature and leakage of vessels，ground fault and the power consumptions of internal and external loads，system diagnoses faults and takes protection measures. The data monitored is uploaded to the remote console located at the shore station though optic-fiber Ethernet. Thus，remote control and management can be achieved by the shore station console. Experimental results validate that the system is reliable and is an important guarantee for the long term operation of ocean cabled observatory.