Abstract: Relying on the Shenzhen-Zhongshan Link immersed tube tunnel project, through large-scale model test, the influence of immersed tube lowering on the extrusion and removal characteristics of fluid mud is studied, and the relationship between the extrusion volume of fluid mud and the base pressure and the density of fluid mud is determined, which provides a reference for the formulation of reasonable dredging standards. The main conclusions are as follows: ① The earth pressure under the immersed tube increases with the increase of the displacement of the immersed tube lowering. The farther the distance from the sludge outlet, the greater the earth pressure on the upper and lower surfaces of the fluid mud layer, and there is an obvious pressure difference in the horizontal direction of the earth pressure, under which the fluid mud is gradually discharged from the sludge outlet; ② When the density of the fluid mud is less than 1.30 g/cm³, all the fluid mud can be squeezed out by increasing the base pressure, but when the density of the fluid mud is more than 1.30 g/cm³, all the fluid mud can not be squeezed out by increasing the base pressure, and there is an obvious marginal decline effect; ③ The extrusion amount of the fluid mud decreases with the increase of the density, and there is an obvious mutation when the density of the fluid mud is 1.30 g/cm³.