Abstract: A seafloor seismic and tsunami monitoring system based on fiber optic interferometric technology was developed and installed in the nearby waters at China's State Oceanic Administration’s (SOA’s) Wuchang (Hainan Province, China) monitoring site. The developed tri-component version of fiber optic interferometric seismometer had a resonance frequency of about 250 Hz, a sensitivity of 57 dB (0 dB represents 1 rad/g), with the operation frequency range of 0.005-50 Hz and the minimum detectable vibration acceleration of 43.4 ng/\sqrt\rmHz , while the fiber optic interferometric water level monitor has an accuracy of ±1 cm, a measurement range of 0-110 m. The system had been operating well more than 4 years since October, 2017, and earthquakes as well as real-time water levels had been recorded during the long-term field trial. From January in 2018 to December in 2021, there were over 60 earthquakes with ML6.0+ in Northeast Asia area, and 39 earthquakes were recorded by our system. As an example, the detailed measurement results about the ML6.8+ earthquake in adjacent waters of the Sulawesi, Indonesia were given. In this paper, we reported on the planning, design, fabrication, laboratory tests, sea installation, observation, data acquisition, and analysis associated with this effort. The system installa-tion process was introduced, the working principle of the seismometer and water level monitor was described, and the typical recorded earthquake and real-time water level monitoring data were presented and analyzed.