Due to the shortage of suitable research methods for real-time and long-term observation of oceans,an innovative approach that can provide abundant power and wide bandwidth is being developed worldwide for undersea instruments.In this paper,we develop a direct current (DC) power system which is applied to a multi-node cabled ocean observatory system named ZERO (Zhejiang University Experimental and Research Observatory).The system addresses significant issues ranging from terrestrial facility to subsea infrastructure,and focuses on using appropriate methods to deal with several key challenges,including delivery,conversion,distribution,and management of power,and heat dissipation in pressure vessels.A basic laboratory platform consisting of a shore station,a primary node in a water tank,and a secondary node in a deep-sea simulation chamber under 42 MPa pressure was built and fully tested.An improved secondary node was deployed in Monterey Bay in Califomia for a deep-sea trial.An 11-day laboratory test and a half-year sea trial proved that the DC power system based on our proposed methods is viable for the underwater multi-node observatory system.