Abstract: Seabed liquefaction is a common phenomenon in marine geological disasters, which not only leads to seabed erosion but also poses significant risks to subsea pipelines, marine facilities, and other structures in the area. At present, available studies on the mechanisms of seabed liquefaction is based mainly on indoor physical model experiments, and the field observations are very scarce. In this study, we conducted a one-month field observation at the southern tidal flat of Nanhui, Shanghai. An acoustic Doppler velocimeter was mounted at the fixed platform to obtain high-frequency data of flow velocity and water pressure. A self-made pore pressure probe was applied to collect pore pressure data at different depths of the seabed sediments. In addition, we analyzed the response characteristics of pore pressure to wave loading during a winter gale event and calculated the depth of seabed liquefaction. Results show that the characteristics of pore pressure response are affected by tidal level and wave height, of which the trend of total pore pressure response is affected by tidal levels, and the amplitude of wave-induced pore pressure response is affected by significant wave height. The degree of seabed liquefaction in the study area decreased with depth increase. Due to the relatively low significant wave height during the observation period, the liquefaction depth was only a dozen centimeters.