Abstract: Composite bucket foundation is a type of foundation structure developed in the field of offshore wind power in recent years. The research on its sinking characteristics is very important for the successful popularization and application of this kind of foundation. The field test of the sinking process of offshore wind power composite cylindrical foundation is carried out in the eastern sea area of Ru dong, Jiangsu Province. The variation laws of the overall inclination of the foundation, the pressure in the silo, the pore water pressure and earth pressure at the cylinder wall soil interface during the sinking process are analyzed, and the influence of the cylinder wall soil interface contact on the earth pressure response law of the effective interface inside and outside the cylinder wall is discussed. The test results show that the composite cylindrical foundation sinks smoothly to the predetermined elevation of seabed foundation soil under the complex environmental load of real wind, wave and current, and the foundation inclination is 0.018? after sinking; During the sinking process, the pore water pressure of the outer wall of the foundation is affected by the tide level and the drainage conditions of the contact soil layer, and the negative pressure in the cylinder leads to the peak value of the interface earth pressure of the inner wall of the foundation decreasing by about 46.7% compared with the outer wall. In addition, the study also puts forward that the seepage drag reduction effect and soil squeezing drag increase effect of the cylinder wall soil interface are the main reasons for the differential distribution of the effective interface earth pressure inside and outside the cylinder wall. At the same time, the existence of the mud skin at the cylinder wall soil interface can better explain the lag of the effective interface earth pressure response of the cylinder wall when the foundation passes through the silty sand mixed with silty soil. The research results can provide reference for the accurate sinking of composite tubular foundation under complex geological conditions.