Abstract: This paper introduces the current situation of constructing the seafloor geodetic network from design, layout, measurement, and data processing. Based on the requirements of national ocean strategy and the development of marine geodetic technology, the problems of the construction of seafloor geodetic networks at the present stage are analyzed. According to the results, it can be concluded the coverage of the current seafloor geodetic network is limited, and the information sharing is insufficient. In addition, the design and layout principles are not combined with the positioning precision of the network, which are mostly qualitative descriptions and lack operability. The accuracy and resolution of the sound velocity field are low and the measurement and data processing are difficult to meet the requirements of large-scale and high-precision underwater PNT (positioning, navigation and timing) network construction. To solve the mentioned problems, the concept of constructing the underwater PNT network with remote communication, information interconnection and telemetry is put forward. Several key technologies, including the design and layout of the underwater PNT network, the construction of the ocean sound velocity field with high precision and high resolution, the measurement strategy, data processing method and the thought of self-calibration and self-maintenance for underwater control points, the function of target and environment telemetry and sensing services, are discussed to provide support for the new generation of high-performance marine geodetic survey and the construction of underwater PNT network. It is believed that the proposed network system will lead to a revolution in underwater PNT construction when problems such as the optimal design of the large-scale network, enhancing positioning service, the accurate timing and time synchronization, remote communication and the extension of the application are broken through.