Ocean-bottom seismometers represent crucial marine seismic observation instruments. Considering the loud ocean currents and frequent human activities in China's offshore shallow waters, we proposed a chain seismic observation method and designed the mechanical structure of a cabled ocean-bottom seismometer node. First, the overall structure of the seismometer node was designed based on the dimensions and layouts of its internal components. Subsequently, the hull thickness, end cover thickness, and sealing dimension were determined based on theoretical calculations and finite element simulations. Finally, a pressure test verified the pressure resistance and water tightness of the designed seismometer node structure, while a comparative seismic observation test validated the structure's ability to detect natural earthquakes. Considering these accomplishments, the designed cabled ocean-bottom seismometer is planned to be deployed for actual seismic observations in the offshore area of the Zhejiang Province to gather real-time and continuous seismic observation data.