An underwater environment real time monitoring system with high reliability, strong operability and good real time performance for an experimental ocean observatory network was designed and realized in order to monitor the deep sea underwater environment real timely. The mechanical structure of pressure vessel was designed based on theoretical arithmetic and stability check. The distribution of the temperature field inside the cavity was obtained through building heat dissipation model and utilizing the approaches of ANSYS software simulation and sensor measure. A surge current suppression method with a mechanical contactor and a power resistor in parallel was proposed to realize effective surge current limitation and a reliable start up. Network time protocol (NTP) and precision time protocol (PTP) were adopted to achieve high precision time synchronization, in which time packets were exchanged between the time server on the shore station and the underwater system, and sub microsecond precision time service could be obtained. Upper computer software based on VC++ was developed to realize real time controlling and monitoring the unerwater system. The specific function verifications of all the sections of the system were conducted in the laboratory, and the system was deployed in the South China Sea in a sea trial. The results indicate that the developed system is effective, reliable, and suitable for deep sea continuous operation.